Abstract: The major oceanographic characteristics of the eastern Pacific warm pool(EPWP)and the relationship between the variation in the EPWP and ENSO based on the SST data from 1950 through 2002 are analyzed.The results show that the form and thermal state of the EPWP obviously exhibit the seasonal and interannual variations related to the ENSO cycle.The heat content,the area and the southern edge of the EPWP are all closely related to the ENSO.The composite analysis indicates that the heat content decreases,the area lessens and the southern edge is located at the northernmost position in the preceding year for El Nino onset,while the heat content increases,the area enlarges and the southern edge shifts to the southernmost position after El Nino onset;during the La Nina,the variation trends of the heat content,the area and the southern edge of the EPWP are contrary to those during the El Nino Besides,the meridional displacement of the EPWP may play an important part in the development of the ENSO.