A 6-layer,4°×5° horizontal resolution global ocean model has been designed and improved.After a 100-year in-tegration,an equilibrium state has been reached from the upper to lower layers.By taking the mean state of last l0 mod-el years as climatic state,we analyzed the characteristics of the seasonal variation in our model integration.The resultsshow that the simulated seasonal variation is similar to the observed.So the design of our model is successful.Then,us-ing the simulated climatic state of the seasonal variation as the initial state,and the observed stress and thermal state asthe atmospheric forcing,we simulated the process of El Nino in 1972—1973 successfully.The simulated results of sea-sonal variation using our model will be presented in part I. A 6-layer, 4 ° × 5 ° horizontal resolution global ocean model has been designed and improved. After a 100-year in-tegration, an equilibrium state has been reached from the upper to lower layers. By taking the mean state of last l0 mod-el years as climatic state, we analyzed the characteristics of the seasonal variation in our model integration.The result shows that the the simulated seasonal variation is similar to the observed. So the design of our model is successful. Chen, us-ing the simulated climatic state of the seasonal variation as the initial state, and the observed stress and thermal state asthe atmospheric forcing, we simulated the process of El Nino in 1972-1973 successfully. The simulated results of sea-sonal variation using our model will be presented in part I.