In this paper, with the original cyclone bag filter and the composite bag filter of No. 1 active carbon powder negative pressure pneumatic-conveying system for the active carbon flue gas purification project of Baosteel No. 3 sintering plant as the study object, the numerical simulation research for the internal flow fields of the two types of bag filter were conducted by using Computational Fluid Dynamics (CFD), and the flow distribution coefficient of tube sheet holes were also calculated. The simulation results well explain the cause of filter bag mouth damage of the cyclone bag-filter, and meanwhile they also indicate that, the internal air flow distribution and the tube sheet hole flow distribution of the composite bag filter after improvement and with addition of flow guide plates are more uniform.