The effects of various factors on the radiation -induced emulsion polymerization of styrene in soap-free system and the kinetics of growth of latex particles have been studied. It has been found that the monomer-water ratio influence on the rate of polymerization (R,P,) and the stability of latices, and rate of polymerization is proportional to dose rate (I) to the 0.5 power, i. e., R,P,∝I,0.5,. The activation of this polymerization system is 7.5 kcal/mole. The molecular weight of polymers are with in the range of 10,4,~10,5,. The molecular weight distibution of polymer latices is narrower than that of polymer latices obtained in chemical-initiated emulsion systems.,On some specified condition, monodisperse particle size, "clean" latices can be obtained. The mechanism of emulsion polymerization in soap-free system have been suggested.