Using semi-continuous seed polymerization method, a novel acrylate latex water repellent modified with organic silicon was prepared with multi-vinyl silicone oil (Si(Tri)),3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TRIS), methyl methacrylate (MMA), butyl acrylate (BA) and acrylic acid (AA) as monomers, cationic octadecyl polyether acrylate trimethylammonium chloride (OATAC) and nonionic isomeric tridecanol polyoxyethylene ether (DNS500) compound as emulsifier, 2,2'-azobis (2-methylpropionamidine) dihydrochloride (AIBA) as initiator and glycidyl methacrylate(GMA) as cross-link agent. The influence of mass ratio of Si(Tri) and TRIS，dosage of GMA and organic silicon monomer on the performance of latex ,water contact angle, water absorption of latex film, and water repellency performance of cotton fabric finished by these latexes were investigated. The results showed that this latex particles displayed core/shell morphology obviously, when the dosage of organic silicon monomer was 30%, mass ratio of Si(Tri) and TRIS was 25/75, and dosage of GMA was 2%, the water contact angle was 115.75°，water absorption was 3.23%(12h), and the cotton fabric finished by this latex exhibited excellent water repellent property with 90 points.