The integrated and single teeth meshing stiffness are calculated by tooth contact analysis and load tooth contact analysis under assembly misalignment. A corner meshing impact calculation model is put forward considering contact ratio, and 12-degree of freedom nonlinear double helical gear vibration model is established considering meshing stiffness, corner mesh impact, and backlash. Take the ship transmission system as an example, verified by changing the contact ratio. Teeth contact ratio is changed by adjusting tooth height modification coefficient, the meshing impact model in this paper is proved effective through comparing to calculation results in the literature [8]. The results also show that under the constant load, the system's vibration reduce with the increasing contact ratio; however, when contact ratio exceeds the value 4.07, vibration shows increasing trend.