Abstract: Using the NCAR CAM3 model, we designed several sensitive experiments to simulate the response of the atmospheric circulation and precipitation in June to SST anomalies (SSTA) over the equatorial Eastern Pacific. Firstly, we constructed idealized SSTA based on the observational SSTA over the equatorial Eastern Pacific during September 1997 to June 1998. We performed the first series of sensitive experiments by incorporating the idealized SSTA in different durations, that was, from the preceding September to June, the preceding October to June, the preceding November to June, the preceding December to June, January to June, May to June, June. Secondly, on the basis of the SSTA in the first series of experiments, we changed the SSTA by adding or substracting 0.5 ℃. The second series of sensitivity experiments were conducted to simulate the precipitation response to the intensity of SSTA persistent from the preceding September to June. Finally, the SSTA in the second series of experiments were changed from positive to negative, and the third series of sensitive experiments were done. The precipitation anomaly averaged over the area (25°-30°N,110°-120°E) was used to represent the rainfall anomaly in the Yangtze River basin and its southern area (YRBS). We found that， (1) the precipitation response to El Ni?o with different durations varies with the maximum rainfall anomaly appearing in November and the minimum in June. The anomalies of the precipitation attenuated when the duration is shorter, meaning that the strong SSTA in the preceding autumn affects most significanty rainfall in the YRBS. This confirms previous diagnostic analysis results. (2) The precipitation anomalies over the YRBS are not sensitive to the intensity of the equatorial Eastern Pacific SSTA. There is always obvious positive precipitation anomaly over the YRBS under strong or weak SSTA. The area coverage of the positive precipitation anomaly agrees with the observation, suggesting reasonable model results. The intensity of the precipitation anomaly increases with that of the SSTA. (3) When opposite SSTA are put in the model, the simulated results are different from the results of the diagnostic analysis for a La Nina event. Negative precipitation anomaly could be reproduced only when the negative SSTA are intensive enough.