Abstract: The HEPA filter is an important equipment for air purification in nuclear power plant.The internal air flow uniformity will directly affect its service life,and thus affect the air purification efficiency.In this paper,the flow field in the HEPA filter is simulated and analyzed by numerical simulation,and the porous medium model in accordance with Darcy’s theory is adopted for the filter element.On this basis,by changing the inclination angle of the upper and lower walls of the filter housing and changing the inlet cross-sectional area,the sensitivity of the filter structure and inlet wind speed is analyzed.The numerical simulation results show that the inclination angle of the upper and lower walls of the filter has little effect on the air flow uniformity in the filter.The inlet airflow velocity has a great impact on the internal air flow uniformity.The smaller the inlet airflow velocity is,the better the internal uniformity of the filter is.The simulation results show that controlling the inlet airflow velocity at about l0m/s has a good effect on considering the air flow uniformity and equipment size.