Cationic quaternary ammonium salt fungicides are commonly used in oil fields. In polymer drilling fluids, quaternary ammonium salt fungicides often react with polymers and lose their bactericidal effect. Therefore, it is necessary to develop fungicides that are not easy to react with polymers used in drilling fluids. In this study, benzyl chloride and diethylenetriamine were used as raw materials to synthesize low molecular weight organic amine fungicides. The optimal process scheme of synthetic fungicides was determined through single factor experiment and orthogonal design experiment. When the solute mass fraction was 50% and the reaction medium was 1, When the reaction temperature of 4-dioxane is 53 ℃, the reaction time is 2 h, and the stirring speed is 130 r/min, the reactant conversion rate can reach 94%. The bactericide was added to the polymer-containing wastewater for evaluation. When the dosage was 60 mg/L, the bactericide rate could reach 99.2%.