Based on the theory of modal analysis, aimed at the structure characteristic of the gear transmission system, establishment of involute spur gear 3D model and finite element model using 3D modeling and finite element simulation software. Through the simulation calculation, analysis of the low order natural frequency and main vibration mode, the results show that: the first 6 valence vibration gear is the main vibration and torsional vibration. The vibration, the more violent, so in the design of gear system should be as much as possible to avoid the low order natural frequency reaching gear.