The mulsifier-free polymerization with semi-continuous adding method with small quantities of the self-made polymerizable emulsifier is studied . The soap-free emulsion is synthesized by methyl methacrylate, vinyl cyanidevinyl cyanide, butyl acrylate, 2-hydroxyethyl acrylate and acrylic acid. The preparation of coating process is not easy demulsification by using soap free emulsion,and the coating has a good adhesion with the substrate. In the application experiment of soap-free emulsion ,the influence of emulsion type, glass transition temperature and the type of primer on the film appearance, adhesion and resistance to salt fog performance are analysized. The physical and chemical properties of self-made soap-free emulsion are evaluated by testing appearance and all kinds of stabilities of the emulsion, and the glass-transition temperature of the self-made soap-free emulsion is determined according to DSC. The results are shown that the self-made soap-free emulsion has good stability, and the self-made soap-free emulsion has basically reached the industrial application effect. Because of no the interface effect of emulsifier， hard and soft monomer proportion of soap-free emulsion in 1.4, there is good adhesion, film density, excellent resistance to salt fog. The waterborne coating of cabin finish is fine and close by using the soap free emulsion. And soap free emulsion which is high glass transition temperature has good resistance to salt fog within 500 hours, while the glass transition temperature is lower, in the 1000 hours salt fog effect is more outstanding. It is shown that the finish has excellent adhesion with different primers and good resistance to salt fog performance.