The recent development of carbon fiber sizing agent was introduced in this article. The sizing agent used in carbon fiber was synthesized at a temperature range of 55-60°C using epoxy resin and vinyl acetate as a monomer together, octyl phenol ethoxylated(OP-10) as the emulsion agent, ammonium peroxydisulfate as the solicitation agent and water as the dispersant. At the same time, the optimum composition, the optimum process condition and the effects affecting the emulsion stability were discussed. The characterizations were measured by Scanning Electron Microscopy and TG. The results show that the synthesis process is simple, low cost, less polution and remarkbably stable. The diameter of the particle is 1.8μm and the decomposition temperature is 260°C.