The computational fluid dynamic simulation of the airflow inside a bag filter was carried out, three optimized structures of the hopper were proposed to improve the original hopper structure. The flow characteristics of the airflow inside the bag filter were obtained. The effect of airflow distribution of three optimized structures were compared with original structure. The results showed that the airflow in the hopper of the original structure formed an impinging jet. The maximum velocity was 8.3 m/s, and the minimum velocity was only 0.5 m/s, the relative root mean square velocity of the monitoring surface was 0.99. The velocity distribution on the corresponding monitoring surface was extremely uneven along the mainstream direction. The airflow uniformity inside the bag filter was improved in all three optimized structures, thus it was possible to improve the airflow uniform distribution by adding baffles. Considering the airflow uniform distribution inside the bag filter, adding vertical baffles was optimal, which can be improved by 41.41%. However the uniformity of the optimized structures with the third tilted baffle or the straight plate with a wing were not significantly improved compared to the addition of vertical baffles. Therefore when the hopper structure is optimized, the influence of the deflection of impinging jet on the airflow distribution inside the hopper can be neglected.