A nonlinear dynamic model of fatigue crack of gear teeth was built an d its parameters were determined by checking standard and tolerance of pair gear . The model not only has broader adaptability, but also ensures veracity of para meters in theory and high precision. The simulation results from the fault model indicate that frequency multiplication is indispensable as well as the fault ch aracteristic frequency due to existence of eccentricity. The results also show t hat the larger the load of gearbox is, the clearer fault characteristic frequenc y will become. The results provide a theoretical basis for the faults diagnosis of gearbox and frequency spectrum analysis of vibration signals.