The relationship between the daily number of people with heatstroke and meteorological factors is studied by using the interval averaging method on the basis of the daily heat stroke case data and meteorological data from 1994 to 1998 in Wuhan. The results reveal that maximum air temperature is the key factor for the occurrence of daily heat stoke events, and relative humidity and total cloud cover are also relevant factors; the daily mean number of people with heat stroke increases exponentially with increasing daily maximum air temperature, slowly from 31 ℃ to 34 ℃ and abruptly from 35 ℃ to 39 ℃. A simple fivegrade criterion for heat stroke is devised, and five weather types and the corresponding indexes for heat strokes are determined according to the analysis and the combined types of daily maximum air temperature with daily relative humidity, minimum air temperature, and total cloud cover, which can be used as an important supplement for the grading prediction of heatstroke indexes and can be applied to the whole Yangtze Drainage Basin.