Guangzhou city with a large population and urban size located in the Pearl River delta, Guang Dong province, China, was chosen to study the effect of urban heat island and its spatial expansion. The land surface temperature was analyzed and divided into 7 ranges by a temperature separation method based on statistical results. In the case of urban area, it was composed by three parts: downtown and old built-up areas with high-density buildings and dwellings, new built-up areas and developing site. Along with the city development, the developing site will become to be new built-up areas and the formerly new built-up areas will become to be the downtown and old built-up areas. These three parts stand for different stages of a city. By temperature partition using the standard deviation, we can commendably find the corresponding ground covers, and three parts of the city are properly within three surface temperature ranges. Based on this, the thermal remote sensing image can be used to detect the developing stage of the built-up areas in a city. Temperature comparison of different land covers was also analyzed and showed a great difference between them. The white soil is almost 3 degrees higher than the urban area, while the water is more than 5 degree cooler than it.