Abstract: This invention concerns the preparation of certain polyester, which includes amino acid in backbone, and active drug in side chain. It has the general formula as follows: wherein R1 is aspartic acid, serine, glutamic acid or lysine; R2 is active drug with reactive group. The preparation of this polymer has three steps: firstly the polymerization of lactide or lactone with derivative of morpholine-2,5-dion, secondly the deprotection, finally the bonding with drug. Through introducing amino acid comprising reactive group to biodegraded polyester, the antigen of the degraded result can be avoided, and it can be absolutely bioabsorbed. Because polymer includes carboxyl, hydroxy and amido, it can have effect directly, or after being degraded. This invention can be used as the coating of medical instruments, and can be prepared for the implant or other regent.