Abstract: In order to ensure the reliable ventilation and safe operation of the underground coal gangue separation workshop, numerical simulation was carried out on the air flow field in the underground coal gangue separation workshop by using FLUENT software, which provided a theoretical support for its rational ventilation. A three-dimensional physical model was established according to the layout of the underground coal gangue seperation workshop in Changcun Mine, the air velocity distribution at each location under different air quantity conditions was simulated and analyzed, and the minimum requirement for air quantity was determined. Through the analysis of the air flow field, the corresponding breeze and eddy area was found out. Based on the minimum requirement of air velocity, the breeze and eddy in this area can be completely eradicated by taking the measures such as changing the local design of the roadway and adding the air deflectors, in such a way, the safe production in the mine can be guaranteed.