The work aims to investigate the effect of the change of the pumping pressure during the filling process of the valve bag on the powder movement in the package, the concentration of flying powder, the particle capture rate, and the compactness of the package and find out the optimum filling process with the typical industrial powder lithium hydroxide as the research object. Based on the gas-solid coupling mechanism, the Realisable k-ε turbulence model and discrete phase model in Ansys Fluent were used to simulate the filling and pumping process of the valve bag under 5 different pumping pressure. The particle capture rate, compactness in the package, and flying powder concentration were set as the evaluation criteria. Increasing the pumping pressure caused particles to be collected near the filling extraction port, and improved the concentration of flying powder in the package, the rate of particle capture, and the compactness of the package at the same time. When the pumping pressure was 0.04～0.06 MPa, the flying powder concentration and particle capture rate in the valve bag were relatively low, and the compactness of the package could reach more than 90%. By setting an appropriate range of pumping pressure, the flying powder concentration and particle capture rate in the bag can be guaranteed to be low during the powder filling process, and the appropriate compactness in the package can also be guaranteed.