Abstract: Using different polypropylene powders, the residence time distribution was determined by pulse trace method in the cold model experimental apparatus of a horizontal stirred bed reactor (HSBR) equipped with different kinds of stirring paddles. The experimental data were simulated with multi-level model of the whole mixed reactor in series and two-parameter model, respectively. The results demonstrate that the back-mixing degree of leaf blade agitator was the maximum and most close to a fully backmixed flow; the back-mixing degree of T-type agitator was the minimum, and most close to the plug flow.