Abstract: In order to study the effect of the flat baffle inlet distortion on the internal unsteady flow field of the fan, SST k-ω turbulence model was used to simulate the three-dimensional flow in the whole flow passage, including the intake air duct, of a mining contra-rotating main fan. The internal flow field characteristics are analyzed in detail. The results shows that compared with the undistorted intake type, the flat baffle inlet distortion deteriorates the flow field in the intake air passage upstream, resulting in the decrease of the relative flow angle of the impeller inlet and blocking the blade passage in the distortion zone, and the rotating stall of the contra-rotating fan will occur in serious cases. The vortex pair located under the lower passage caused by the flat baffle inlet distortion leads to a serious difference in the static pressure load distribution of the two blades in the same distortion area, which seriously affects the working state of the impeller and blades. Along the span of the entire blade, the flat baffle inlet distortion has the most serious impact on the blade tip area.