Abstract: The process of mining and ore crushing generates a lot of dust. Bag filter is an effective equipment to remove particulate matter from dusty airflow. However, there is a problem of uneven distribution of air volume in the filter bag during operation. The existing way of adding deflectors in bag filters increases the complexity of its structure. In order to solve the problem of uneven distribution of mass flow of middle box lower inlet filter bag, a method of filter bag mass flow even distribution by adjusting selected bags’ permeability is proposed. Firstly, realizable k-ε equation model is selected to simulate the flow field of model bag filter. Then, the numerical simulation results are compared with model experimental results, which verifies the correctness of the simulation method. After that, a geometric model of filter bag with 160 filter bags installed in the middle box is established. Flow field characteristics, mass flow distribution and uniformity of the filter bag at the face velocity of 0.5～1.2 m/min are analyzed by numerical simulation. Finally, taking the uneven distribution of filter bag mass flow at 1 m/min face velocity as an example problem, a method to reduce the permeability of filter bag at the outlet side with large mass flow is designed. According to the Darcy formula and pressure drop calculation formula of filter material, relationship between permeability and filter material thickness, fiber diameter and filling ratio are given. The results show that under this research model, the increase of face velocity will make the mass flow distribution of the filter bag more uneven, and the mass flow of the filter bags on the outlet side of the bag filter will gradually increase. Reducing the permeability of 8−10 rows of filter bags in the area with high flow rates from 2.0×10⁻¹¹ m² to 1.7×10⁻¹¹ m² can reduce the root mean square deviation of mass flow distribution of filter bags from 0.158 to 0.099. The increase in the initial pressure drop of filter bag is 6.1%, proving this method is feasible. In the process of making filter material, the permeability of filter material can be adjusted, so it is feasible to make the mass flow distribution of filter bag uniform by adjusting the permeability of filter bag in selected area.