Abstract: A three-level baroclinic ocean model has been developed for studing large air-sea interaction, climate and climatic change. The formulation of the model is based on the primitive equations with the hydrostatic and Bousinesq approximations. The numerical integration is done in two phases. In the first phase, the model was integrated starting from an rest state over ten years under the annual mean wind stress. At the end of the first phase, a quasi-equilibrium state in the upper levels was reached. The simulated results show that the major large scale feature of annual mean temperature field and main currents in the tropic Pacific Ocean, such as the narrow belt of cold water and strong upwelling in the equatorial region, the South Equatorial Current, North Equatorial Countercurrent and Undercurrent, have been reproduced. Then by using the results at the end of the first phase as an initial condition, and using She wind stress in winter and in summer as upper boundary conditions, we carried out an integration for one year. It is shown that the seasonal variations of the ocean currents are apparently relatad to the seasonal variation of trade wind system. Simulated Equatorial Countercurrent is strong in summer and weak or disappeared in winter. The South Equatorial Current which located in the north of the equator is stronger in winter than it is in summer, but the one in the Southern Hemisphere is strong in summer and weak in winter.