The El Niño/La Niña and the Southern Oscillation (ENSO) is an interannual
phenomenon involved in the tropical Pacific ocean-atmosphere interactions. In this article, the aim is to create an asymptotic solving method of nonlinear equation for the ENSO models. And on the basis of a class of oscillator of ENSO models, using the method of homotopic mapping, the approximation of solution of corresponding problem is studied. It is proved from the results that homotopic method can be used for analyzing the SST anomaly in the equatorial eastern Pacific and the thermocline depth anomaly of the atmosphere-ocean oscillation for ENSO model.