Based on the radar echoes,information of weather conditions and the catastrophe in Shandong prvince,the correlation between the top height of echo vault H_m,severe echo vault region H_z,the strength of the echo vault Z and the hail fall probability was analysed. The discrimination indices of the hail in single and bi parameter were provided. The parameters formula incorporating with conditional probability of hail was used to identify hail cloud. It showed the use of the three parameters discriminatory index for hail forecast. This is very important for the forecasting of severe convective weather.