The improved multigrain model was used to simulate the gas phase polymerization of butadiene catalyzed by low-, medium-, and high-activity catalysts, respectively. For the low-activity catalyst, the mass and heat transfer resistances in the particle were negligible. The morphology of the polymeric particles was uniform. For the medium-activity catalyst, the overall mass transfer effectiveness was > 90%, the maximal temperature rise was 8K, and the heat transfer resistance in the particle was negligible. Mass transfer resistance does not affect the morphology of product particle significantly. For the high-activity catalyst, the overall mass transfer effectiveness was within the range of 70-96%, the morphology of the product particle was affected by the mass transfer resistance to some extent. The maximal temperature rise was 21K; the heat transfer resistance in the particle was negligible as well. However, there was some severe mass transfer resistance in the particle, and the maximal temperature rise was less than or equal to 30K for the large catalyst particle with the same activity. Thus, the polymeric particle morphology was comparatively poor, with the occurrence of particle softening and sticking.