Modeling of a reactor for bulk styrene polymerization in industrial manufacturing processes has been studied. The continuous industrial reactor system was composed of three reactor units; a prepolymerization reactor(e.g. stirred tank reactors), a main reactor with horizontal multicompartmented reactors and a tubular reactor for transportation of the viscous polymerizing liquid. In this study, the multicompartmented reactor was assumed to be cascade of CSTRs. The industrial continuous reactor model was presented and its performance was compared with industrial data. The industrial data indicated that the model was quite satisfactory in describing the polymerization rate and polymer molecular weights. It was shown that the proposed reactor model could be used to find the polymerization process conditions to produce high molecular weight polymers.