The adjustment of the equatorial Pacific thermocline to an initial extratropical thermocline anomaly is studied using analytical and high-resolution (1/16¿) primitive equation numerical models. It is found that the fast adjustment due to the coastal Kelvin wave and equatorial Kelvin and Rossby waves, and the slow adjustment due to the eastern boundary planetary wave play important roles in the redistribution of the initial anomalous mass, thereby determining the phase and magnitude of the equatorial thermocline transition induced by the initial extratropical thermocline transition. For a given extratropocial anomaly, both analytical and numerical models show that the equatorial thermocline transition occurs about 2--5 years later, and the magnitude is about 5--10% of the initial anomaly. The mean circulation in the North Pacific intensifies the transition of the equatorial thermocline and reduces the phase-lag of extratropical-tropical thermocline transition. ¿ 2000 American Geophysical Union