The invention belongs to the technical field of polymer, and relates to a preparation method of microgel composite hydrogel, which comprises the following steps: preparing solution containing N-hydroxymethyl, preparing dispersion solution, preparing prepolymerization solution, polymerization and heating and crosslink at high temperature. Acrylamide is adopted as a main monomer, N-methylol acrylamide is used as a functional monomer, the prepared microgel dispersion solution containing the N-hydroxymethl is adopted as a potential crosslink agent, and then the microgel composite hydrogel is prepared with a method of first polymerization and later high-temperature processing and crosslink. The method is free from adopting chemical modifier to obtaining the microgel containing the potential crosslink point, so the preparation process of the microgel composiste hydrogel is simpler, and the mechanical performance of the prepared hydrogel is excellent.