The solvent-free cationic silicone modified polyurethane /polyacrylate composite emulsion(PAU) were prepared by isophorone diisocyanate(IPDI),polytetrahydrofuran glycol(PTMG1000), N-methyldiethanolamine(MDEA), trimethylolpropane(TMP) and othermaterials, with silane coupling agent (KH550) . The chemical structure of PAU and properties of emulsions were characterized by FT - IR , TG, XRD, TEM and so. The results showed that : when n (-NCO): n (- OH) = 1.07, m (St): m (BA) = 1:2, MDEA content was 5.50%, TMP content was 0.55%, KH550 content was 0.69%, it synthesizes polyurethane with the expected structure, and the addition of silicone enhanced flexibility of the membrane.