A preparation method of a polyether sulfone functional separation membrane supporting a dendritic polyamide-amine functional group includes the steps of: 1) performing chloroacetylation and aminationmodification treatment to polyether sulfone successively and preparing chloroacetylchlorine-diethylenetriamine-polyether sulfone separation membrane chips; 2) with methyl acrylate and ethylenediamineas main reagents, performing modification to the membrane chips by means of Michael addition and amidation reactions with plasma irradiation grafting synergistic technology; 3) preparing the polyethersulfone functional separation membrane supporting the dendritic polyamide-amine functional group via phase-transfer technology. The method is simple, wherein the grafting efficiency of the dendriticpolyamide-amine functional group is high. The functional group has large supporting quantity in the separation membrane, is stable in the separation membrane and is not liable to lose. The polyether sulfone functional separation membrane can remove heavy metals and phosphates in water body high-effectively and has a board application prospect in the field of water pollution control.