Multidisciplinary coupling among dynamics, tribology and elastic mechanics (strength and stiffness of crankshaft) on a crankshaft-bearing system of a diesel engine with four pistons, which was applied on a rated load, was studied by self-designed program as well as the software of ADAMS and ANSYS. The Miner’s theory and accumulative damage theory have been applied in calculating on fatigue strength of the crankshaft. It showed that there are obvious differences in calculating results between the coupling analysis and the traditional non-coupling analysis. The coupling analysis is necessary to improve the working reliability and its mechanical performance of a diesel engine because the various mechanical behaviors of a crankshaft-bearing system happened simultaneously with the engine working.