A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation(SOR) iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime. A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications. Gas-groove dry-gas seal to fluid the dynamic pressure effects to realize the seal and lubrication processes, while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out. There is little research into the effects and the influence on seal performance, if the grooves and the gas films are at the micro-scale. This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation. The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation (SOR) iterative method. The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure. Numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects. the open force is enlarged, while the gas film stiffness is significantly decreased due to micro-scale effects. friction and power consumption remain constant, even in low sealing pressure and spin speed conditions.In this paper, the seal performance at different rotor face spin speeds is also described. proposed proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance, which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.