Abstract:In past years it is believed that El Nio comes from warm water events of equator east Pacific Ocean. But in recent years, we find that the sources of El Nio Warm water and La Nia cold water are both near the the thermocline of warm pool of Tropical West Pacific. After they get stronger , they propagate to east along the thermocline. When they arrive the surface of equator east pacific, and they become so-called El Nio and La Nia. On the other hand, when the warm water of El Nio goes east along the equator, the cold water of equator east pacific goes north to northern latitude 10, near the northern equator ocean current, and propagate to west, finally arrive the subsurface of warm pool, and become the source of cold water of La Nia. So we get the conclusion that there is a movement circle of cold and warm water in the sub-surface in Tropical Pacific. Then El Nio and La Nia alternately appear.