The monodispersed microspheres copolymerized with styrene (St) and bismethacryloyloxyphenylpropane (BVA) were prepared by emulsion polymerization and emulsifier-free emulsion polymerization. With the crosslinking copolymerized microspheres as seed, a series of foamable core-shell PS particles containing different foamable substances were synthesized. And they were of different crosslinking degree and particle diameters. The effect of the foamable substance on polymerizing dynamics and the microsphere structure in the seed swelling process was characterized by TEM．The structure and thermal decomposition dynamics of the foamable particles were also studied. The composite blowing agent was of the self-nucleated characteristic. The mechanism of the foams’ nucleating, growing, stabilizing and controlling in the process of dynamic extrusion foaming was studied, and the limited free form extrusion process was invented. Used the new process, the perfect low-foam profile, sheet, and pipe which were of the uniform foam structure, lower density, high intensity, and glabrous surface were prepared. The produces have been extended to multi-area of the country and have gotten favorable economical and social benefit.