Hydrolysis behavior of block polyester PBS- PPS under different pH conditions was studied. The degradability, surface morphology and crystal morphology of the copolymer before and after degradation were also discussed, which demonstrated that with the increasing amount of PPS segments in PBS - PPS block polyester, the material degradation rate increased. The degradation rate under different pH conditions was as follows: alkali environment (46.15%) > acid environment (33.45%) > neutral environment (11.46%). The degradation process of polyester film started from the membrane surface and was prior to degrade amorphous region. With the increasing of PPS segments, the crystallization radius of the material was reduced, which mainly due to the introduction of PPS hindered the crystallization of PBS. The experiment result of hydrolysis under different pH conditions was consistent with hydrolysis mechanism for block polyester PBS- PPS. Under the alkali environment, hydrolysis was complete. However, under the acid environment and neutral environment, the hydrolysis of ester bond was accompanied with its reversible reactions.