Air was used as the working fluid,and based on computational fluid dynamics method,a 3D unsteady numerical simulation of the oil-free air scroll compressor under variable operating conditions was carried out.It is found that the radial gap between the orbiting and fixed scroll teeth will make the distribution of temperature,velocity and pressure in the working chamber of the compressor irregular;increasing the rotational speed can not only increase the mass flow of the scroll compressor,but also reduce the amount of tangential leakage,thereby improving the working efficiency of the compressor;if the discharge pressure is too large,it will reduce the basic output performance of the scroll compressor;at low rotational speed,the excessive discharge pressure will make the compressor occur a “net backflow” phenomenon at the outlet.