Abstract: The auther derives, in the light of the assumption of isothermal flow in the nozzle and the slot, the mathematical model of the pressure of the gas film in aerostatic bearings. The pressure value of the gas film could be obtained quickly by computers, and the load capacity of aerostatic bearings could be calculated. The exactitude of this mathematical model has been proved by tests. Experiments show that the effects of the circumferential flow of the gas film is remarkable. The auther conducted an inquiry into the computation, provided by Powell and Shires, of load capacity of aerostatic bearings.