In order to accurately establishing helical gear dynamic model, and well knowing vibration characteristics of helical gear system, meshing stiffness calculation method is put forward based on load tooth contact analysis and considering shaft torsional deformation. Analyzing the helical gear dynamics models established by the decomposition of the mesh stiffness in major domestic literature, and illustrating it’s violation of theoretical mechanics. Based on decomposition of the force and vibration displacement, helical gear vibration model is established consdering meshing stiffness excitation and corner mesh impact excitation. Take the helical gear transmission system as an example, the results consistently indicate that the method based load tooth contact analysis can easily and accurately calculate the teeth meshing stiffness. The dynamic response of literature[8] are significantly different from theory of actual. The results based on decomposition of the force and vibration displacement are good agreement with the theoretical actual.