Abstract: A new concept of vertical energyhelicity(VEH ) index is proposed,and its physicalmeaning is explained.In order to prove its  effect,by using the NCEP(1°×1° )reanalysis data and the important weather data of MICAPS,the vertical energy helicity index is applied to a thunderstorm in front of trough which took place in the northof China from July 4 to 7 in 2009 .Furthermore,its universality is proved by using four cases taking place in the north of China in summer from 2008 to 2009 .The result shows that the vertical energy helicity index can re flect the ability of unstable energy releasing from spiral ascending process and has better superiority in forecasting thunderstorm than other indexes.Generally,if the VEH index is large rthan 1.4 J·m·kg^-1·s^-2 at 14 :00 ,a thunderstorm will happen within 3-6 h.