The characteristic and regularity of urban heat effect of Guangzhou City are analysed by using statistical method in this paper.The author points out that there are obvious diurnal and annual variations in intensity and frequency of urban heat effect with time in Guangzhou.The maximum intensity and frequency occurs at 8 p.m.in a day and during November and December in a year.The maximum intensity magnitude of urban heat effect in the set of 0.1—1.0℃,whose frequency is 45%.Probability which occurs when the urban heat effect is larger than 0.1℃ is 60%.Moreover the weather condition and temperature variation have great effects on the urban heat effect,which is intensified in fine weather and usually has a high random frequency in occurrence,vice versa in cloudy weather.In winter the urban heat effect is ganarally weakened when the temperature becomes higher and intensified lower temperature.On the contrary,in summer it is intensified when the temperature becomes higher a and weakened lower temperature.