Abstract: An intermediate ocean model for tropical Pacific is employed to investigate the influences of the different seasonal background on the variations of the sea sur face tem perature anomalies on ENSO time scale.The control experiment has been carried out,in which the ocean is driven by an anomalous wind-stress fields that involve the seasonal cycle.The sensitivity experiments are conducted,in which the ocean is for ced by the same wind-stress anom alies but under a backg round of a special season such as spring.It is found that El Niño/La Nina events do appear in any season,which indicating that the existence and maint enance of El Niño/La Nina does not depend on seasons.Inequatorial western Pacific in the model,the disturbances of subsur face tem perature that propag at eseast ward are evidently leading in phase to the SSTA of east ern Pacific.This is useful for us to understand the mechanism of ENSO cycle and to improve ENSO predictions.The amplitudes of SSTA are different under different seasonal backgrounds.The SSTA in NINO3 region during boreal spring (winter) as the climate backg round case is obviously bigger (smaller) than that of control case.Further,if the SSTA in winter season is not big enough,the El Niño/La Nina event will disappear because the winter season background tends to reduce the magnitude of SST anom alies.