PAE/St/BA copolymer emulsion has been prepared with unsaturated PAE resin, styrene and butyl acrylate by means of emulsion polymerization in the presence of ammonium persulfate as initiator, Tween-80 and OP-10 as emulsifier. The structure and properties of the copolymer were studied by FT-IR, TGA, Zeta potential measurement and particle size analyzer, static contact angle and SEM. The effect of the dosage of unsaturated PAE resin on properties of the copolymer were discussed in the paper. The results show that the excellent performance and good sizing effects of PAE/St/BA copolymer emulsion were achieved when the reaction conditions are as follows: the dosage of unsaturated PAE resin is 3% in polymerization and the dosage of the surface sizing agent was 0.6%.