Actually, it's not at all close to the Poema de Mio Cid, which I entered for Project Gutenberg back before Distributed Proofreaders was devised. The movie is far closer to the French play by Pierre Corneille.

In the traditional literature, for example, the Cid is an old man when he dies, having well before taken revenge on his sons in law for mistreating his daughters and seeing them with higher ranking second husbands. Not the little girls in the movie (which is one of my favorite big screen epics, despite having small connection to tradition).

The Mocedades de Rodrigo (Youthful Deeds of Rodrigo, c.1360), does set up the death of Jimena's father and some other elements in both Corneille and the movie, and some only used in the movie, like the duel over Calahorra. However, the Mocedades is considered the youngest of the Spanish chansons de gest, shading overr into the later medieval form called the romance. Considering it ends with King Ferdinand and the Cid conquering in war France, the Pope, and the Holy Roman Empire, I think we can say it falls outside the bounds of the historical.