Obvious urban heat island effect has been developed at the Pearl River Delta urban group for the last ten years. The annual urban heat island intensity rose from 0.1℃(1983) to 0.5℃(1993). The urban heat island intensity of the Pearl River Delta urban group has obvious monthly difference and daily difference,it is the strongest in November,but the weakest in April. The urban heat island intensity during the nighttime is stronger than that during the daytime for annual-average. For spatial distribution,the intensity in the center part is stronger than that in the ambient part,which closely correlated with economical activity.