Abstract: The oceanic feature in the tropical Pacific Ocean one year before the two types of ENSO event was analyzed. The results show that, one year before the eastern pattern El Nino events onset, the La Nina events occured, in which the SST was extremely colder than normal in eastern and central tropical Pacific Ocean; one year before the eastern pattern La Nina events onset,the El Nino events occured, when the SST was extremaly warmer than normal in eastern and central tropical Pacific Ocean. There were much warmer SST in the tropical western and central Pacific Ocean before the Central pattern El Nino events onset, and much colder SST in the tropical eastern Pacific Ocean before the central pattern La Nina events onset. Warmer SST in the tropical weatern Pacific warm pool region is an essential condition for the onset of central pattern of El Nino events.