Abstract: Based on the elastic fluid dynamic lubrication theory, a three-dimensional lubrication simulation model of the main bearing was built with AVL Excite Power Unit software for 2D25 type horizontal diesel engine, which had been designed and developed independently. According to the elastic deformation of bearing bush and bearing seat and the roughness of bearing bush and journal, the impacts of the bearing clearance, width, oil inlet position and the oil groove width on the main bearing lubrication characteristics were investigated. The results indicated that the bearing clearance and the bearing width were the main influence factors and made great effects on the main bearing lubrication among the four structural parameters, while the oil inlet position and the oil groove width were the secondary influence factors. With the rising of the bearing clearance, the average load, average moment, peak oil film pressure and average oil outflow quantity of bearing increased and the minimum oil film thickness and average friction power consumption were reduced. With the increase of the bearing width, the average load, average moment, peak oil film pressure and average oil outflow quantity of bearing decreased and the minimum oil film thickness and average friction power consumption increased. There is no significant regularity of the effects of the oil inlet position and the oil groove width on the main bearing lubrication characteristics.