In order to further improve the numerical simulation accuracy of the multi-reference frame(MRF) model of cooling fan, the roughness of the model was modified by the wall function, and the influencing factors of the MRF model were analyzed. Firstly, the algebraic relationship among roughness constant, roughness height and y+ is obtained based on the dimensionless velocity u+ and distance y+ of the first layer mesh from the wall in the viscous sublayer. Then, according to the actual wall type, the revised y+ value and the first layer mesh height are obtained, and they are brought into the standard wall function for near wall correction. Finally, taking a cooling fan as an example, the effects of turbulence model, mesh number and surface roughness correction on the numerical simulation results of the fan are studied. The results show that the model can deal with the flow with high strain rate and bending streamline better, and is more suitable for the rotating flow of fans, and has higher accuracy for the simulation of rotating machinery such as fans. Over-dense mesh number will make the calculation results fluctuate; surface roughness correction improves some abnormal points on the performance curve, and within the range of fan common operating conditions, the deviation between test value and simulation value is increased from 5% to 3% after correction.