Preparation method of lactide-glycolide copolymer

The invention provides a preparation method of a lactide-glycolide copolymer. The preparation method comprises the following steps: (1) lactic acid dehydration: heating and dehydrating lactic acid to obtain dehydrated lactic acid with the moisture content of 2wt% or below; (2) prepolymerization reaction: adding the dehydrated lactic acid and glycollic acid into a reactor with a condenser tube according to the proportion of comonomers in the lactide-glycolide copolymer for prepolymerization, and controlling the temperature of the condenser tube in two sections, so that lactide steam, lactic acid steam and water vapor are respectively condensed and respectively received and weighed; determining a reaction endpoint according to the amount of condensed water, and calculating the loss amount of lactic acid according to the total amount of condensed lactide and lactic acid; and (3) condensation polymerization: adding lactide with the amount corresponding to the lactic acid loss amount into a reaction product in the