The index for identifing the hail clouds was obtained based on the data fitting of heights of 45dBZ radar echo and the monthly averaged heights of zero-temperature level for 231 convective clouds in 165 days from 1991 to 2003 at Baoji radar observation.The index is defined that if the height of 45dBZ echo of a developing convective cloud at 0800BST ≥ 2.9km of monthly averaged zero-temperature level height,then the hail will occur.The analysis of radar echoes of hail-bearing clouds show that the higher the base of 45dBZ radar echo,the earlier the hail clouds can be identified,and the higher the top of 45dBZ radar echo,the sooner the hail occurs.The formation of hails generally started in the middle part of hail cloud,supper cell,and multi-cell,and then extended upwards and downwards.With the proposed index,the averaged early time indentification is 12 minutes for hail clouds,and 18 minutes for supercell storms,and 22 minutes for multi-cell storms and supercell storms of squall lines.Those times will be helpful for preparation of hail suppression operation.