A series of poly(l-lactic-co-glycolic acid) (PLLGA) with different compositions was synthesized by ring opening copolymerization. The chemical structure, phase structure, thermal property, mechanical property and shape memory property of PLLGA were investigated through FT-IR, 1H NMR, GPC, DSC, XRD and tensile tests, and the shape memory microscopic mechanisms were analyzed. The results showed that good mechanical and shape memory properties can be obtained through changing of PLLGA compositions. For PLLGA90/10 and 80/20, the fixed phase was acted by their crystals and the entanglements of molecular chains, while the reversible phase was acted by their amorphous phase. However, for PLLGA 70/30 and 60/40, the fixed phase was only acted by the entanglements of molecular chains. In general, the best shape memory properties were showed by PLLGA 80/20.