The invention discloses a preparation method of micro-branched micro-crosslinked polyacrylamide. The preparation method comprises the following steps: adding an acrylamide monomer of which the mass percent is 20-30% into water; then adding dimethylaminoethyl methacrylate, persulfate, a chain transfer agent, EDTA and manganese acetylacetonate, regulating the pH value to 5-8, and initiating a polymerization reaction at 20-40 DEG C; after 5-10 hours of reaction, taking out a colloid, and performing granulation; and the adding NaOH accounting for 1.5-3% of the mass of the colloid, and performing hydrolysis at 80-100 DEG C for 1-3 hours to obtain the finished product. The micro-branched micro-crosslinked polyacrylamide prepared by the method disclosed by the invention has high viscosity, and has excellent thermal stability and mechanical shearing resistance; and experiments indicate that the viscosity retention rate of the micro-branched micro-crosslinked polyacrylamide disclosed by the invention after mechanical shearing is more than 81%, and the viscosity retention rate after 90 days of aging is 79% or above. The method disclosed by the invention has the advantages of mild reaction conditions, simple operation process, low cost and the like.