POSS/silicone modified polyacrylate fluorine-free waterproofing agent was synthesized by soap-free emulsion polymerization technology and applied to cotton fabric finishing. The effect of the ratio of soft and hard monomers on the emulsion, latex film and its application performance was investigated. The structure of polyacrylate and the size of latex particles were characterized by fourier transform infrared spectrum (FT-IR) and dynamic laser scatterometer (DLS). And the application properties and surface morphology of the finished fabric were characterized by servo material multifunctional high and low temperature control testing machine, softness meter, and scanning electron microscope (SEM). The results showed that when m(BA):m(MMA) was 6:4, the maximum conversion rate of monomer was 96.97%, the gel rate of emulsion was 0.14%, the minimum size of latex particles was 104.8 nm, as well as the latex film had the maximum water contact angle of 114.3? and excellent water resistance. The finished cotton fabric showed excellent mechanical properties, good softness, and its water contact angle was 161?. SEM results showed that functional POSS nanoparticles existed on the surface of cotton fiber. The fluorine-free waterproofing agent endows the cotton fabric with low surface energy and certain rough structure, so that the finished cotton fabric exhibits superhydrophobicity.