Abstract: Adhesion is one of the key factors to maintain safety and stability of train running. Maximum adhesion is related to the friction. The decline of friction results in decrease of adhesion. In fact the friction coefficient mixed lubrication is not only greatly influenced by surface roughness, but also by roughness orientations. However, the previous investigations regarding the effect of roughness orientation on friction coefficient seem to be contradictory. In this paper,the three typical surface roughness orientations, i.e., longitudinal, transverse and rhombus were treated by laser discrete modification technology. The behavior of three patterns of roughness orientations under mixed lubrication were compared to those of without laser treatment. A numerical analysis based on deterministic model with unified Reynolds equation was adopted. Tribology tests with scaled wheel/rail specimens were carried out. It is concluded that the wheel surface with laser patterns greatly enhanced the friction coefficient comparing with the surface without laser pattern. The friction coefficient of rhombus pattern is the greatest one among that of the three laser patterns. The friction coefficient of longitudinal and transverse pattern is almost the same, but the former is a little higher than that of the latter. The friction coefficient is mainly depended on the ratio of asperity contact pressure to the total pressure in mixed lubrication. The orientation effect on friction coefficient is also determined by lateral flow which is highly depended on the geometry of contact region.