Polymethylsilsesquioxane was synthesized using methyl trichlorosilane (CH3 SiCl3) as the main raw material and ethylenediamine as the trapezoidal control agent. The effects of trapezoidal control agent, hydrolysis medium, catalyst, monomer concentration, temperature and other factors on the molar mass and structural regularity of the polymer were discussed, and the optimal trapezoidal control agent and polymerization conditions were screened. The results showed that the ratio of nCH3SiCl3: n ethylenediamine was 1:111, and the product yield was close to 90%. During hydrolysis, the ratio of nCH3SiCl3: nH2O was 1:15, and the product had a high molar mass and good regularity; After hydrolysis, if tetramethylammonium hydroxide is used as a catalyst and the condensation reaction temperature is 35 ℃, if the reaction time is long, the polymer molar mass is high and the distribution is wide; If the reaction time is short, the polymer has a low molar mass and narrow distribution. If acid is used as a catalyst and the condensation reaction temperature is 80 ℃, the polymer molar mass is low and the distribution is narrow.