Abstract: Waterborne polyacrylate (WPA) was obtained by copolymerization of acrylic acid(AA), butyl acrylate (BA), methyl methacrylate (MMA) in solution. Grafted modified chlorinated polypropylene (MCPP) was obtained through modification of chlorinated polypropylene used acrylic acid(AA) and butyl acrylate (BA). Composite primer was obtained by the combination of WPA and MCPP. The effects of the content of AA (compared to the mass of WPA) and the molecular weight of WPA on the emulsion properties were investigated. The optimum content of AA was 12% and the optimum molecular weight of WPA was 20277. The effects of different ratio between WPA and MCPP on the emulsion properties, surface tension and adhesion were also investigated. The results showed that the particle size of the emulsion decreased, the surface tension of the primer increased, the adhesion decreased slightly with the increasing of the content of WPA. When m(WPA):m(MCPP)=3:7, the particle size was 98nm, surface tension was 47mN/m, adhesion was grade 0. The emulsion of the composite primer was stable and the surface properties and adhesion were good. The composite primer has broad application prospects.