Due to the limitation of the available processing technology now,the smallest surface roughness of spiral groove bottom is typically 0.8 μm.In order to research the influence of surface roughness of spiral groove bottom on the performance of dry gas seal,the surface roughness was approximatively equaled to the changing of groove depth,the effects of surface roughness on the opening force and the leakage under the condition of different groove depths and gas film thicknesses were analyzed by an approximate analytical method.Under the operating condition investigated,both the relative errors of the opening force and the leakage at roughness of 0.4 μm and 0.8 μm was calculated respectively,and was compared with the situation of the smooth groove bottom.The results show that the influence of the groove bottom surface roughness on the opening force and the leakage is increased with the increasing of surface roughness,and the influence of surface roughness on leakage is larger than on the opening force.When the groove bottom surface roughness is smaller than 0.4 μm,the relative error of the influence of roughness on leakage is within 7% and on the opening force is within 3%.