Authors:王石, 高山红*Abstract: Based on the Babin model and the sensitivity analysis of Evaporation duct on meteorological input parameters，a new diagnosis method-ensemble diagnosis (Babin_Ens) method - is proposed in this paper benefitting from the idea of weather ensemble prediction. By using this method, a comparison and analysis of the diagnosed result from the measurements on four island stations in the Chinese marginal seas is done． It is found that both root-mean-square error and bias of duct height and intensity for the Babin_Ens method are obviously improved compared to the Babin model，and the averaged bias improvements of duct height and intensity are 23.49% and 19.29% respectively. Numerical forecasts of evaporation duct are conducted by the Weather Ｒesearch and Forecasting (WRF) model with the Babin_Ens method. The averaged bias improvement rates of duct height and intensity get improved respectively by 14.01% and 16.92%. It shows that the ensemble diagnosis method can greatly improve the diagnosis and prediction of evaporation duct.