Monthly mean anomaly data(1969-1998) of mixed layer depth(d_ml) and upper ocean temperature(T_s) are used to analyze the geographic distribution and the seasonal variation in interannual variability of d_ml in the Pacific.Two largest interannual variability zones of d_ml are found in the high latitude area in the North Pacific and in the central western equatorial Pacific.The latter is primarily concerned.The climatic location of d_ml,the correlation between d_ml anomalies and El Nino events,and the eastward propagation of positive d_ml anomalies along the equator preliminarily accompanied with a strong El Nino event are analyzed.