The invention discloses a preparation method of a 
quaternary degradable 
antibacterial agent, and the preparation method comprises the following steps: homopolymerizing cyclic aliphatic 
carbonate monomers containing 
bromine functional groups, namely 2,2-dibromo-methyl 
trimethylene carbonate (DBTC) monomers or copolymerizing the 2,2-dibromo-methyl 
trimethylene carbonate monomers with aliphatic cyclic ester, or copolymerizing the 2,2-dibromo-methyl 
trimethylene carbonate monomers with the aliphatic cyclic ester or dihydroxy 
polyethylene glycol, or copolymerizing the 2,2-dibromo-methyl trimethylene 
carbonate monomers with the aliphatic cyclic ester or single methoxy 
polyethylene glycol; and further reacting an obtained 
polymer with alkylamine, thus obtaining the 
quaternary degradable 
polyester antibacterial agent with antibacterial performance. The 
antibacterial agent provided by the invention integrates the advantages of 
biocompatibility and degradability and not only has good antibacterial performance, but also has no harm to an environment, thereby being an environment-friendly antibacterial material; as an additive, the antibacterial agent provided by the invention has potential application prospects in 
food packaging materials, fibers, coatings, medical field and the like.