Abstract: In order to study the effect of three intake types on the internal unsteady flow field of the fan, the SST k-ω turbulence model combined with the automatic near-wall treatment method is used to simulate the three-dimensional flow in the whole flow passage, including the intake air duct, of a mining contra-rotating main fan for forced type ventilation. The FFT technique is used to analyze the transient pressure change in the two impellers of the fan, and the pressure fluctuation spectrum of flow field in the impellers is obtained. The results show that, compared with the undistorted intake type, both the elbow distortion and the complex distortion intake types seriously deteriorate the flow field in the intake air passage upstream the first stage impeller, thereby significantly reduce the fan performance. Furthermore, the maximum pressure fluctuation amplitude appears in the internal flow field of the second stage impeller, and the non-uniformity of the air flow increases in the circumferential direction.