Disclosed are a biodegradable polymer with a disulfur five-membered ring functional group on a side chain and an application thereof. The polymer is obtained by activity controllable ring opening polymerization of a cyclic carbonate monomer containing the disulfur five-membered ring functional group. The polymer has controllable molecular weight and narrow molecular weight distribution, and is free from protection and deprotection processes. The polymer obtained by ring opening polymerization of the cyclic carbonate monomer in the present invention has biodegradability and can be used for controlling a drug release system. A prepared tumor-targeting reduction-sensitive reversible crosslinking nano-drug carrier supports long circulation in vivo, but is highly enriched in tumor cells and is quickly decrosslinked in the cells to release drugs so as to efficiently kill the tumor cells with specificity. Meanwhile, the biodegradable polymer has application prospects in tissue engineering scaffolds and biochip coatings and the like.
