Based on a gear tooth fracture case,which is caused by diesel engine crankshaft axial movement. Aiming at the situation that it’s difficult to simulate this fault by experiment,the displacement and movement type can’ t be control. And there is no effective method to extract gear load during the crankshaft axial movement for analysis by experiment. By using Creo,ADAMS software,the gear transmission system dynamics simulation model is built and the no axial movement,one-way axial movement and reciprocating axial movement scenarios is simulated. The gear load change rules during the shaft axial movement is got by extracting the shaft displacement,the gear load and analyzing the relationship between them. The shaft axial movement can cause gears over load,amplitude modulation and impact vibration is verified. The feasibility of the study on the influence of spindle axial movement based on dynamics simulation is proved.