The thermal environment and thermal effect is one of the most important contents in city climate and environment researches. The land surface temperature (LST) is an efficient way to research thermal environmental problem of earth surface. Based on the MODIS data in the middle ten days in July 2005, the LST images are retrieved by the generalized split-window algorithm, the distribution image of the thermal field is made by the maximum value composing method. The conclusion indicates that the high temperature distributes mainly in the Pearl River Delta periphery in the early of calefaction. In addition, the calefaction around the river grows fastest-highest. In full flourish of calefaction, the highest temperature appears mostly around the areas where the densities of river net are high. The urban heat island effect is more evident in urbanization and industrialization cities. These findings accord with the recent development situation in Pearl River Delta, and it will do help to the city planning and construction.