In order to study the influence of out-of-roundness of main bearing on bearing lubrication characteristics of internal combustion engine,a flexible multi-body dynamic model of crank-connecting rod mechanism was established for a V-type 12-cylinder diesel engine.Combined with the generalized Reynolds equation model based on mass conservation boundary conditions,the influence of waveform out-of-roundness error of main bearing on bearing lubrication characteristics was analyzed.The research shows that with the increase of the waveform out-of-roundness error of the main bearing,the peak total pressure of the bearing increases significantly,the probability of bearing surface fatigue and adhesion failure is high,and the bearing lubrication state is significantly worse,and the lubrication stability is reduced.However,the main bearing waveform out-of-roundness error has no significant effect on the average total friction power loss.