Abstract: The effects of rubber content, initiation methods and rubber types on the kinetics of bulk graft copolymerization of styrene onto rubber were studied.It is concluded that the low concentration and the cage effect of initiator and the occlusion effect of rubber radical are the main factors on polymerization rate decrease after low-cis-polybutadiene rubber addition by chemical initiation. With the increase of the content of styrene unit of rubber, the influence of rubber addition on polymerization decreased.When the viscosity of rubber was very high, the polymerization would accelerate due to the gel effect. Compared with thermal initiation, the contents of grafted polystyrene and occluded polystyrene were higher with chemical initiation, which resulted in the evident decrease of polymerization rate and an apparent turning point at phase inversion.