CINRAD WSR98D SA / SB and part of C band Doppler algorithm default parameters are same as WSR88D in U.S. The hail index products based on hail detection algorithm usually overestimate probability of hail, severe hail, and hail size in actual operational application. This paper first illustrates that probability of severe hail and hail size in WSR98D algorithm default parameter is from the dataset of 10 severe hail cases during 1992 in Oklahoma and Florida of U.S. The algorithm parameters based on this data overestimate probability of severe hail and hail size, i.e. over forecasting hail occurrence is caused by limitation of the algorithm itself. Without changing the set of hail detection algorithm parameters, combined with early hail algorithm, some environmental parameters and Doppler radar detection characteristics can be used as auxiliary criterion, such as VIL, VIL density, TBSS, etc. According to the physical process of severe hail formation, and under the assumption without losing generality we propose that the 55 dBz range exceeding 100 m2 on the -20℃ layer CAPPI products can be used as supplemental threshold for judging quickly the formation of severe hails.