Abstract: Current wind farm effective roughness models do not fully consider the influence of atmospheric stabilities. To address this problem,an effective roughness model for wind farms with different atmospheric stabilities is proposed by establishing the momentum balance relationship in the wind farm boundary layer and revealing the flow inhomogeneity of wind farms under different atmospheric stabilities. The proposed model is validated by using the large eddy simulation method,and the results show that the proposed model can effectively evaluate the effect of atmospheric stabilities on the flow inhomogeneity and the wind farm effective roughness,and the average error of the obtained effective roughness is about 10%.