Using the ensemble mean prediction results from Zebiak-Cane coupled ocean-atmosphere model based on NCEP/NCAR 925 hPa reanalysis of wind stress anomaly serving as initialization wind to 1997/1998 El Ni〖AKn~〗o event, the 1997/1998 El Ni〖AKn~〗o event is diagnosed on the basis of the thermodynamics.〖JP〗 The results are as follows: (1) Advection term primarily plays an improving role, while the thermodynamic damping term basically plays a decaying or suppressing role in each Ni〖AKn~〗o area during the El Ni〖AKn~〗o event. (2) From Ni〖AKn~〗o 4 to Ni〖AKn~〗o 1+2, the contribution of the zonal advection to SSTA increase varies lightly in such a way that the counterparts of the meridional advection and vertical upwelling flow increase gradually, meanwhile, the suppressing role of the thermodynamic damping term in SSTA increase becomes stronger. (3) Further analysis indicates that zonal, meridional advection and vertical upwelling flow all play important roles in the evolution of 1997/1998 El Ni〖AKn~〗o event, relatively, the contribution of meridional advection is the most notable.