The crankshaft main bearing of a four-cylinder marine power generation diesel engine has been examined based on the multi-body dynamics theory, thermos-elasto-hydrodynamic lubrication mechanism and asperity contact theory, aiming at the reduction of the vibration of the marine diesel engine and the optimization of the lubrication characteristics of the crankshaft main bearing. The lubrication model of the bearing system is established for coupling analysis of dynamics and tribology, obtaining the vibration and lubrication of the five main bearings of the diesel engine crankshaft. It is found that the 2nd, 4th and 5th main bearings of the diesel engine all have the characteristics of boundary lubrication. The influence of multiple bearing parameters on the lubrication characteristics of the main bearings are studied by using the finite element simulation analysis based on the orthogonal test. It concludes that the bearing clearance and oil supply temperature greatly affect the lubrication of the main bearing, followed by the surface roughness of the bearing pad and the oil supply pressure, while the width of the bearing pad is the smallest. The design of the crankshaft-bearing parameters of the original diesel engine is optimized to propose an improved scheme, resulting in a 48.9% increase in the extreme value of the minimum oil film thickness, a 53.2% increase of the minimum oil film thickness and a 21.5% reduction of the asperity contact peak pressure. The lubrication characteristics of the diesel engine are finally improved.