Abstract: Abstract Though tyre and asphalt are low elastic modulus materials, water lubrication resulting from hydrodynamic action would present even the speed is low. For high elastic modulus of materials, such as wheel and rail, water lubrication would present when the speed is over 200 km/h, causing potential unsafety for train operations. Increasing surface roughness will improve the wheel/rail adhesion coefficient. However it is shown that the topography orientation also has great effect on adhesion coefficient when the value of surface roughness is nearly the same under mixed lubrication. In this paper, a numerical analysis based on unified Reynolds equation was adopted. The behavior of three patterns of roughness orientations on wheels, i.e. longitudinal, transverse and rhombus, with high speed up to 500km/h under mixed lubrication were analyzed. The simulation results were compared with the results of the average flow model and the existing experimental results. It is concluded that the adhesion coefficients of wheel/rail decreased with speed increasing, while the adhesion coefficient of rhombus pattern is greater than that of the transverse, and transverse pattern is greater than that of the longitudinal. The adhesion coefficient is mainly depended on the ratio of asperity contact pressure to the total pressure. When the ellipticity k<1 in wheel/rail point contact, the lateral flow effect could not be neglected, the results of average flow model will result in error.