In order to study the influence of surface roughness on the lubrication characteristics of the valve pair of axial hydraulic piston pump motor,the Weierstrass-Mandelbort fractal function was introduced to simulate the surface topography of the surface roughness with different amplitudes.The oil film lubrication model of the valve pair with fluid-solid thermal coupling considering the surface roughness was established,and was solved by the finite difference method and relaxation iteration method.The variation of oil film thickness,oil film pressure,oil film bearing capacity,friction coefficient and other performance parameters with the amplitude of surface roughness were calculated and analyzed.Through the disk-disc friction and wear test of the valve plate cylinder block,the friction coefficient of the valve pair under different surface roughness amplitudes was obtained,and the mathematical model was verified.The numerical calculation results indicate that an increase in surface roughness amplitude can cause an increase in oil film bearing capacity,but it can also lead to an increase in maximum oil film pressure and friction coefficient,resulting in a decrease in friction performance.The results of friction and wear test show that as the surface roughness increases,the friction and wear on the surface of the valve plate is intensified,and the overall lubrication and wear resistance of the valve pair decreases.Therefore,in the processing of the valve plate surface,the surface roughness should be appropriately reduced.