The other response doesn't actually answer the question, so I'll give it a go.

At the time of the beginning of the Second Sino-Japanese War, the National Revolutionary Army was composed of several types of formations. Very broadly, they are divided into the German-trained divisions, the regular divisions, and the Chinese Communist units (such as the 8th Route Army).

The German divisions were organized much along the lines of the post-WWI Reichswehr, with a size of around 10,000 troops, equipped with German rifles, German helmets (the Stahlhelm) and German training. There were about 8 of these divisions fully battle-ready and another 12 divisions with at least some training. These divisions were just as capable as the Japanese troops, with the Chiang Kai-Shek rifle superior to the Japanese Arisaka, although Japanese divisions were twice the size of Chinese divisions, so to achieve force parity the Chinese would need to employ two of the German-trained ones.

The regular trained divisions were roughly 5,000 troops each and were extremely diverse, ranging from poor warlord levies essentially conscripted from local peasants to elite warlord troops equipped with light tanks, Muslim Hui cavalry on par with Japanese cavalry, to sundered formations of other Chinese troops mix and matched together into a new unit.

The Communist divisions had a mix of Chinese, Soviet, and captured Japanese equipment. They were very well-trained, but they were underutilized in the war due to the Communist desire to preserve their strength, instead mostly participating in guerrilla actions.

The actual performance of the Chinese troops was quite good. The Japanese predicted that they could achieve a rapid victory within 3 months. Instead, it took them three months to break out of Shanghai, partly due to an ill-advised political maneuver by Chiang Kai-Shek to send his best German-trained troops into an urban struggle in Shanghai to attract the attention of the foreigners in Shanghai's concessions, hopefully leading to Western intervention. In doing so, however, he severely attritioned these units, to the point that they were unable to take advantage of the defensive fortifications protecting Nanjing, which would likely have severely hindered Japanese efforts further.

Still, even with this strategic error, while the Chinese were giving ground, the Japanese were also being attritioned, namely in their fuel and other tools required to wage war. The reason for the Japanese invasion of the Dutch East Indies-and for the Pearl Harbor operation-were to acquire the supplies necessary to continue the war in China. This led to the Japanese attempt to cut off the supply route to China via the Ledo-Paoshan Burma Road, which severely impaired Chinese troops-as did the withdrawal of German aid in 1938-but was supplanted by the Allied "Hump" air-supply operation.

Indeed, by 1945, the situation had so improved that the Chinese had defeated the Japanese units in southern China and as the atomic bombs were dropped were in the middle of a massive operation to roll up the Japanese flank all the way to Shanghai. While there was certainly infighting, corruption, and self-interest that hurt the Chinese war effort, the National Revolutionary Army was still quite a powerful defensive force, especially against a lightly mechanized force like Imperial Japan.

Size wise, a Chinese division, at full strength, was 9000 guys, more often than not, a Chinese division hovered at around 5000-6000 soldiers. A standard Japanese type B infantry division at full strength was 19,000 guys. A Japanese independent or mixed brigade was 9000 - 10000 soldiers. It's why when people talk about the Japanese "only" having 30 some divisions and a couple brigades in China it's a bit misleading. These were gigantic formations.

Equipment wise, the disparity was worse.

A Chinese division was lucky if they had any artillery and what they would have would be mountain guns and smaller caliber stuff. They lacked ammunition and the only thing that might be encountered in abundance were rifles, mortars and light machine guns. (The Czech ZB-26 was THE machine gun of the Chinese Army. They received 30,000 of them and produced them domestically as well). Chinese divisions lacked trucks and pack animals, by and large.

The 200th was the only Chinese division with an armored component, but read what they had in 1938. The Tank regiments had 70 T-26's 4 BT-5's, 20 CV-33 tanks. The armoured car regiment had around 50 BA Armoured Cars and 12 Sd Kfz 221 armoured cars. Besides, it had more than 400 Ford trucks. The motorised infantry regiment used Soviet trucks and rifles, and the artillery regiment had 12 122 mm howitzers, also 45 mm anti aircraft artillery and 75 mm field guns. That division was exceptionally well equipped and it's got the attack power of a poor quality Italian motorized division.

A Japanese division, by contrast, would have an independent field artillery regiment as well as a smaller artillery regiment attached directly to the main infantry brigade. They also had a dedicated Engineer regiment, a dedicated transport regiment, and a dedicated cavalry regiment. A Japanese division, especially in the 1937 - 1943 period, could also replace any lost equipment far more easily than the Chinese could.

Training wise: the Japanese were of far higher quality. People would accuse the Japanese of being rigid tactically, but they were generally good tactics. (Later in the war, the tactics that they had perfected fighting the Chinese would fail them spectacularly against the better equipped and trained US forces.) The Japanese had very good staff colleges and could produce junior officers who were competent and experienced. The basic Japanese soldier was also literate. Japan actually had one of the highest literacy rates of any country in the world during the pre war period.

The Chinese, by contrast, were not as gifted. First of all, China only had a 15 to 25% literacy rate and the most educated and modern segment of the population had fallen under Japanese occupation when the Japanese took the coast. So suitable officer candidates were in short supply. As for the officers that the Chinese did have, one third of the Chinese army's officers had gone to Baoding Military academy in Beijing which had been founded in 1902 and closed in 1923. It gave some modern training and most of the officers from the north went here if they were old enough. (Chiang Kai Shek went here for a semester before going to Japan in 1906. In Japan, he attended an Imperial Japanese Army Academy in Tokyo and then served in the Japanese army for 2 years, returning when the Qing dynasty fell. It made the Allied refusal to listen to him even weirder since he actually was trained in Japanese doctrine and tactics.) In 1924, the KMT used Soviet provided funds to found Whampoah Military Academy (properly pronounced Huangpu) in Guangzhou, and Chiang Kai Shek cemented his rise to power by being the commandant of the Academy. Students here learned from Soviet instructors initially during the first five years and then a mixture of Soviet and German instructors during the 30's. Officers who had graduated during the 30's were generally quite competent, but there were only a couple thousand of them for an army of millions. (It's like Germany's problem of having to stretch the trained 100,000 of the Versailles Treaty to the entire Heer.) Half of China's officers went to Whampoah and Chiang Kai Shek generally didn't trust generals who hadn't gone to Whampoah. That said, Whampoah was lost to the Japanese with Guangzhou in 1938 and most of the competent junior officers died in Shanghai. The rest of ther generals went to various foreign (mostly Japanese) or local military academies or had no formal military training at all.

Within the Chinese army, generals tended to only promote subordinates who went to the same academies that they had. This was not very helpful to fighting quality and it sometimes led to weird outcomes. For example, there were 97 Chinese officers who went to US military academies from 1900-1937. When they returned, they had trouble finding good postings because of the above system. What ended up happening to a lot of them was that the Chinese Finance Ministry, under Columbia graduate Kong Xiangxi, was allowed to form a few tax enforcement divisions. Kong Xiangxi then invited an American trained officer whom he knew from Columbia to head one of these up, and then he in turn brought in more American trained officers to fill out the lower ranks. These finance divisions would then be made regular army in 1937. In Burma, there was one of these divisions, the 38th led by Sun Li Ren, and the British were often surprised when a random Chinese colonel from that division would respond in perfect New England English.

Now put all this together, and the Chinese army had to be super conservative about attacking because the failure points across any given conglomeration of Chinese troops were so many. Not surprisingly, most of China's victories during WW2 were in defensive battles(the four battles of Changsha over five years). So China lost many more soldiers than the Japanese, however each Japanese soldier held a higher degree of importance to the Japanese war effort than the individual Chinese.