This work aimed to study the effects of branched monomer on the polyacrylate emulsion. A branched polymer (HBP4) was synthesized by esterification using maleic anhydride and pentaerythrite. And then it was neutralized with ammonia water. And the emulsion was synthesized by emulsion polymerization using methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA) and the branched polymer aqueous dispersions as comonomer. The particle size distribution of the branched polyacrylate emulsion was in the range of 100-200nm, surface tension stabilized at 30~35 mN/m, and it had film-forming property and the emulsion had good stability. This branched polyacrylate emulsion had low viscosity and high stability. Adding branched polymer as monomer to the polyacrylate emulsion could decrease the viscosity of emulsion and the water absorption of latex film.