The grafting copolymer (PLA-g-CDA) was prepared by using Sn(Oct)2 as catalyst and grafting meso-lactide onto the cellulose diacetate in the vacuum melting environment. The copolymer was characterized using FTIR, DSC and stretching test. The effects of feed weight ratio, catalyst content, reaction temperature, reaction time and reaction atmosphere on the monomer conversion and grafting ratio were examined. The film compatibility and mechanical properties of the grafting copolymer were then evaluated. The results showed that in the vacuum reaction environment, feed weight ratio of meso-lactide and cellulose acetate was 4∶1, catalyst content was 5%, reaction temperature was 140 ℃, reaction time was 30 min, and grafting rate of the product was higher. With the increase of PLA grafting rate, PLA-g-CDA was filmed more easily, and the compatibility as well as the mechanical properties was improved.