The　carboxyl-terminated　modified　polylactic　acid　copolymers　of　P(LA/SA),　P(LA/CA)　and　P(LA/AC)　were　synthesized　via　directly　melt　polycondensation　with　D,　L-racemic　lactic　acid　(D,　L-LA)　as　raw　material　and　stannous　octoate　as　catalyst.　The　copolymerization　reaction　was　performed　at　the　temperature　of　168°C　and　the　pressure　of　0.098　MPa　using　linear　heating　method.　The　copolymers　were　characterized　by　viscosity-average　molecular　weight,　FT-IR,　1H-NMR,　DSC,　TGA　and　XRD.　The　results　demonstrate　that　Tg　of　the　carboxyl-terminated　copolymers　is　lower　than　PLA,　reducing　the　rigidity　of　PLA;　the　copolymers　have　good　thermal　stability　for　one-step　thermal　decomposition;　compared　with　PLA,　the　crystallinity　of　P(LA/SA)　and　P(LA/AC)　decreased,　while　the　P(LA/CA)　slightly　decreased,　so　that,　by　adjusting　the　ratio　of　lactic　acid　and　modifier　to　adjust　the　mechanical　properties.