Poly(butylene methylsuccinate) (PBMS) was prepared using methylsuccinc acid (MSA) and 1,4butanediol (BD) as raw materials. On this basis, the new copolyesterpoly(butylenes terephthalatecobutylene methylsuccinic acid) (PBMT) was synthesized via melt polycondensation from adding dimethyl terephthalate (DMT) to PBMS. The intrinsic viscosity, molecular weight, acid value, hydroxyl value, chemical structure and thermal properties were investigated by means of ubbelohde viscometer, FTIR, 1HNMR, DSC and TGA. The results showed that the intrinsic viscosity and molecular weight reached the maximum while the acid value and hydroxyl value reached the minimum under the conditions that n(DMT+MSA)/n(BD)=1.00∶1.08, n(DMT)/n(MSA)=1∶1. The best copolyester can be synthesized when TBOT and zinc oxide were used as complex catalyst. FTIR and 1HNMR demonstrated that the PBMT was synthesized successfully. DSC and TGA revealed that the thermal property of PBMT had greatly improved compared with PBMS.