To estimate the agglomeration weight for emulsion polymerization conducted in an agitated vessel, a simple method of combining a preliminary experiment and a CFD analysis is proposed. To get the relation between agglomeration weight and shear rate, the emulsion polymerization of interest (we adopted the styrene polymerization) was conducted in a vessel consisting of two-axial cylinders, which provides almost constant shear rate throughout vessel. To predict the shear rate experienced by a liquid or polymer, the trajectories of particles were obtained by CFD for the actual agitator adopted for emulsion polymerization. Employing these results, the agglomeration rate in emulsion polymerization in the real agitator equipped with a Maxblend could be estimated. The estimated result of agglomeration weight for emulsion polymerization shows good agreement with the experimental result conducted in the actual agitator.