In order to study the effect of in-cylinder gas on the performance of the whole engine after escaping into the crankcase through the piston ring set, the relevant mathematical model was established based on the thermodynamic theory of internal combustion engine, including the diesel engine performance calculation model, the gas leakage model and the wear model. The gas leakage model considered the effect of gas leakage on the performance parameters under the influence of the piston ring gap, and the effect of cylinder linerpiston ring wear on internal combustion engine performance was studied based on equivalent opening clearance. Finally, the overhaul period of diesel engine was predicted according to the law of performance degradation based on the Archard model. The calculation results show that the power declines by 7.52% and the specific fuel consumption increases by 7.73% under rated conditions when the maximum wear of cylinder liner is 400 μm and the first piston ring wear is 200 μm.