Heat waves appear usually accompanied by both the abnormal high temperature (or high temperature and muggy weather) and a persistent period of high temperature weather. According to these two characteristics, heat wave index is designed as an identification index of heat wave weather to show the torridity extent and accumulative effect of high temperature process, and the classification standard of heat waves is established. Heat wave index and meteorological grades were tested by daily numbers of heatstroke sufferers in Wuhan during July to August of 1994 and 1995 and daily numbers of death in Shanghai during July to August of 2003. The results show that the heat wave index is a valid index to predict heat wave weather. The method on grading of heat wave can be applied to the actual operation.