A 3-D nonlinear contact analysis model with several teeth pairs in meshing which is used to simulate a pair of cylindrical helical gear in the large power shipborne reducer is established by the direct constraint method provided by MSC.Marc. Then, based on the model, a quasi-static analysis is carried out in a meshing period. The numerical results show a very good agreement with the meshing rules in reality, and simultaneously, the rationality of the model is verified. Because of the original traits, the model can be used to be deal with the dynamic meshing problem of the gear pair.