The camshaft is an important component that ensures the timely opening and closing of valve in marine diesel engines. Due to the poor contact lubrication state and excessive friction excitation， it is easy to cause larger interface torque on the camshaft. Considering the effects of transient excitation and interfacial friction， the tribo-dynamics model of the valve camshaft in V20 diesel engine is established. The forced vibration results of the camshaft are obtained， and the friction and lubrication performance of the cam-tappet pair is also analyzed under the fluctuating speed. The results show that， by thoroughly considering both the transient ex? citation and frictional excitation of each cam pair， the additional stress in each shaft section of the valve camshaft increases by about 4 MPa， while the transient speed fluctuation at the camshaft end increases by roughly ±30 r/min. Under the combined effects of speed fluctuation and surface roughness， the film thickness is dramatically reduced in some positions， especially in the cam base cir? cle section where the film thickness decreases by about 0.3 μm. At the reverse motion position and nose of the cam， the tempera? ture rise at the interface of the tappet exceeds the material’s scuffing temperature， thereby increasing the risk of scuffing wear.