Abstract: The structure of the three-pad sliding beam air foil bearing is analyzed. The mesh of the foils is divided into mixed elements, and the stiffness matrix of the foils is calculated based on the principle of minimum potential energy and the nonlinear thin plate theory. The finite difference method is used to deal with Reynolds equation, and the distribution of gas film pressure is calculated. Finally, the fluid-structure coupling of gas film pressure and foil deformation are calculated by weak coupling method. The calculation process is determined, the calculation program is written, and the accurate calculation of gas film pressure distribution, sliding beam deflection and bearing limit load is realized. Combined with concrete examples, the effects of rotor speed, bottom foil thickness, bearing position angle, number of sliding beams and width distribution on bearing capacity are deeply studied. The relevant regularity curves are obtained, and the corresponding analysis of these results is carried out, which can provide a theoretical basis for the optimal design of foil gas bearing. The results show that the increase of the number of sliding beams will reduce the minimum film thickness of the bearing, and the increase of the stiffness of the sliding beam at the axial symmetry plane can increase the bearing limit load. Reducing the bearing mounting angle can reduce the rotor eccentricity, but also can reduce the bearing limit load.