In this paper, the polystyrene (PSt)/laponite composite was prepared by in-situ emulsion polymerization, and the compatibility between laponite and PSt was significantly improved by the chemical modification of quaternary ammonium salt on the laponite. Effects of the modification degree of laponite on the properties of the composite latexes and corresponding composite materials were investigated by TEM, SEM, XRD, DSC and TGA. In addition, the PSt/laponite composite latex was introduced into a poly(styrene-co-butyl acrylate) latex to form the composite latex films, and the properties of the as-prepared films including tensile strength and water vapor permeability were investigated. It is found that the modification degree of laponite is the key factor to influence the preparation and property of the composite latex. Introduction of laponite has obvious effect on the glass transition temperature (Tg) and heat resistance of PSt, the tensile strength (Rm) of the latex film obtained by introducing the 5% PSt/laponite component into the PSB system is increased from 8.3 MPa to 14.8 MPa, and its water vapor permeability is improved 19% compared with the latex film obtained by adding the same proportion of unmodified PSt/laponite composite emulsion.