Abstract: By use of cluster analysis in this paper,the monthly averaged SST of the North Pacific is objectively gouged into ten types that have the totally changing characteristics mainly with the changing artanalies of the Mid-East Equatorial Pacific.We can group them into El Niňo-type and La Niňa-type according to the ENSO pherxmerxm.These two types include typical field,non-typical field and three transitional fields.The typical one has the good persistence and fits correctly the EI Nino and La Niňa occurring from 1951 to 1996.Within half a year,there is not inter-conversion between the two typical fields;however,the non-typical field compensates to typical one when it enhances or weakens.The transitional type persists poorly.It is rarely possible for the same transitional types to inter-converse.The main transitional types for conversing are Type 3 and Type 9.By using the type the presern SST field belongs to plus the change of index,it is expelled to predict the beginning and the declination of El Niňo from 1 to 2 months in advance.