The friction and wear of journal bearing mainly occurs in the starting and stopping stage.In order to study the tribological performance of journal bearing under start-up condition,a numerical analysis model of mixed lubrication for journal bearings was developed.Reynolds equation with mass conservation boundary condition was used to solve the fluid pressure,Greenwood and Tripp contact model was used to predict the solid surface contact,and Johnson load distribution concept was used to connect the lubrication model and contact model,so as to realize the tribological behaviors of journal bearings from mixed lubrication to hydrodynamic lubrication under start-up and shut-down conditions.By this developed model,the starting and stopping performance of journal bearing system was analyzed under three different lubrication conditions,the boundary lubrication,mixed hydrodynamic lubrication and hydrodynamic lubrication.With the journal bearing system as an example,by combined with different functions of the bearing speed,the influence of the acceleration performance of the bearing on the start-up performance of the bearing was analyzed.The effects of working conditions,oil temperature and bearing structure on the start-up performance of the bearing were studied.The results show that the larger starting acceleration of the bearing can help the bearing enter the hydrodynamic lubrication faster.Higher rotating speed,lower lubricating oil temperature and larger bearing clearance can make the bearing have a better performance in start-up stage.