It is a "de partitif." In French, if you say "de + article," it could mean "of the" but it could also mean "some." So if you write "il mange la viande" you are saying "he is eating THE meat". 他吃那块肉 However, if you add "de" and write "il mange de la viande", you are writing "he is eating SOME meat." 他吃一些／一点肉