To what extent does the mean climate influence the simulation of the El Niņo Southern Oscillation (ENSO) phenomenon? In this present study, our hypothesis is that, with a better mean state, the simulation of interannual variability will be im-proved. A state-of-the-art coupled climate model, the Community Climate System Model Version 3.0 (CCSM3), is used for this study. Three experiments are de-signed to improve the simulation of mean climate in CCSM3. In Experiment A, a time-independent empirical correction is used in surface heat flux at the air-sea in-terface. In Experiment B, the depth of sunlight penetration into the ocean is changed. Experiment A is an empirical correction of the biases in the mean climate simulation, whereas Experiment B tests the sensitivity of the mean climate to the sunlight absorption in the upper ocean in a physical process. Experiment C is a combination of Experiment A and B. The simulations of annual mean, annual cycle and ENSO in these two experiments will be compared with observations and control CCSM3 run to examine whether the mean climate has an impact on the simulation of ENSO.