Blending modification of poly（propylene carbonate）(PPC) and Blending modification of poly（propylene carbonate）(PPC) and polylactic acid (PLA) was finished, thermal performance, mechanical properties and biodegradability were raised. Properties of composites were studied by SEM, XRD, DSC, TG and tensile test. The results showed that no chemical reaction had occurred, and blends were partially compatible. Thermal properties of PPC were improved. The optimal Tg of composites was 30℃ higher than that of PPC. The optimal Td5% of composites was 42℃ higher than that of PPC. The optimal Td50% of composites was 67℃ higher than that of PPC. With PLA addition the degradation of composites was better than that of PPC. After 40 days degradation, the largest weight loss rate of composites was 33.37% which was 9 times of that of PPC. The PPC-PLA composites had good film forming ability and the film transparent and uniform. The tensile strength of composites ranges from 36 to 58MPa. The maximum young's modulus of composites was 2943MPa.