In this work, a seeded soapless emulsion polymerization was carried out with crosslinking (XL) poly(methyl methacrylate) (PMMA) as seeds, styrene as monomer, and potassium persulfate (K2S2O8) as initiator to synthesize the PMMA XL-PS composite latex, which we knew as the latex interpenetrating polymer network (IPN). The morphology of the latex IPN was observed by transmission electron microscopy (TEM). It showed a core-shell structure. The kinetic data from the early stages of the reaction of seeded soapless emulsion polymerization showed that the square root of polymer yield (W-p)(1/2) was proportional to the reaction time. The reaction rate decreased with the increase of crosslinking density of PMMA seeds. The core-shell model proposed in our previous work(1-2) was modified to predict the conversion of polymerization over the entire course of the synthesis of PMMA(XL)-PS composite latex. Our modified core-shell kinetic model fitted well with the experimental data.