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采用熔融缩聚法制备聚乳酸，并先后通过亚磷酸三苯酯扩链、聚乙二醇共聚分别制备扩链聚乳酸（PLLA-T）和聚乙二醇改性聚乳酸(PLEG)。研究了聚乳酸分子量、材料组成、分子结构对聚乳酸降解性能的影响，讨论了不同条件下聚乳酸的降解行为。结果表明：聚乳酸在氢氧化钠溶液中降解速度最快，在磷酸盐缓冲液中降解最慢。相对分子质量越小，降解的越快。PLEG的降解速度最快，其次是PLLA，PLLA-T降解速率最慢，亲水基团的存在，加快降解速度，提高了PLEG共聚物的降解速度。“,”Polylactic acid (PLA) was prepared by melt polycondesation, and then extender chain PLA (PLLA-T) and polyethylene glycol modified PLA (PLEG) were prepared with Triphenyl phosphite as chain extender and polyethylene glycol as copolymer composition, respectively. The effects of molecular weight, composition, molecular structures on the degradation performances of PLAs were studied. The degradation behaviors of PLAs under different conditions were discussed. The results show that the fastest degrading of PLA is in NaOH solution,and then is in HCl solution, the slowest is in Phosphate buffer slution. The smaller the relative molecular weight, the faster the degradation. The fastest degradation is PLEG, and the slowest is PLLA-T among PLLA, PLLA-T, PLEG. The existence of hydrophilic group speed up the degradation, improved the PLEG copolymer degradation rate.