Aiming at the wear problems of camshaft and idler gear sliding bearing in diesel engine driving mechanism, the fault reason was analyzed by simulation and test methods. The analysis shows that the camshaft gear sliding bearing is located at the end of oil supply and in the state of boundary friction or even dry friction at the moment of diesel engine start-up, which is the main cause of abnormal wear. The failure reason of idler gear bearing is that the improper lubrication structure leads to poor lubrication and wear. The improvement is then proposed, and the abovementioned problems are hence effectively solved according to the comparative analysis, which can provide the reference for the design and fault analysis of driving mechanism sliding bearing.