The work state evaluation of the piston-cylinder group is significant for maintaining a good working condition and reducing the failure rate of the internal combustion engine. Taking an engine cylinder-piston group as an example, the piston slap motion in the cylinder is simulated. According to the simulated results of piston slap motion parameters, the surface wear state and wear clearance of the piston cylinder group are evaluated, and the influence of the cylinder-piston clearance variation on the piston slap motion characteristics is analyzed. In the end, the variation laws of different dynamic parameters of piston slap motion in the cylinder are obtained on the condition of different existing cylinder-piston wear clearance variation. The results also show that the proposed analysis method in this study can effectively predict the piston slap motion variation law caused by the wear clearance variation of the engine cylinder-piston group.