Abstract: Under the combined influence of various influencing factors, the crankshaft will have axial motion along the axis direction of main bearings while it rotates in the actual operation of an IC engine. Taking the crankshaft-bearing system of a four-cylinder four-stroke IC engine as the research object, considering the axial motion, crankshaft deformation and surface roughness, a new lubrication model of the crankshaft main bearing was established based on the average Reynolds equation. The influence of axial motion of crankshaft on lubrication performance of crankshaft main bearing was studied. In the analysis, the motion law of the crankshaft along the bearing axis was measured by the test method, and the finite element method was applied to solve the tilting of the crankshaft in the bearing bore caused by the crankshaft deformation. The results show that the axial motion of crankshaft had a significant influence on lubrication of crankshaft main bearing with a rough surface. The journal center trajectory of main bearing was an unclosed three-dimensional space curve when the axial motion of crankshaft was taken into account. The degree of influence of the axial motion of crankshaft on the lubrication characteristics of the main bearing was directly related to the surface roughness. The influence trend and degree of the surface roughness on the lubrication characteristics of main bearing were obviously changed when considering the axial motion of crankshaft.