Urban water bodies are mainly classified into natural water and artificial water. As an important part of urban ecosystem, it plays an important role in relieving Urban Heat Island (UHI) effect. It is important to study the current status of urban heat island effect, explore the buffer effect of water body on urban heat island, and provide theoretical basis for urban transformation and planning rational for improving urban heat island effect and ecological environment. The area considered in this study was the north-south direction of Changsha's Xiangjiang River, located in Changsha downtown. Based on Landsat 8 TIRS remote sensing image of Changsha City in July 2016, the land surface temperature (LST) was retrieved by atmospheric correction method. The synchronous urbanization process and land use types were obtained by supervised classification method, and the spatial distribution characteristics of surface temperature and heat island effect in urban areas were analyzed. At the same time, the buffer effects of Xiangjiang River on the thermal environment and various buffer zones in Changsha City were analyzed by building multi-scale buffer zones on both sides of Xiangjiang River and overlapping them with land surface temperature and land use types. The results showed that: (1) the spatial distribution of urban construction pattern in Changsha City was basically similar to that of heat island effect. The heat island effect of built-land was higher, and the extreme surface temperature reached 53.8 C. The heat island effect of water, green space and bare land was relatively low, and the lowest surface temperature was 16.0 C. (2) The Xiangjiang River had a buffer effect on the heat island effect in Changsha, and the average buffer distance for the heat island effect in Changsha was 400 m. (3) The buffer capacity of the Xiangjiang River to the heat island effect was related to the type of land cover around the water body. The buffer effect to the east of the river was less than that to the west of the river, and the buffer effect to the leisure area along the river was greater than that of the residential area along the river. In summary, the intensity of heat island effect in Changsha city is related to land use type, moreover, the heat island effect of construction land is serious. The buffer effect of water body on heat island is significant, but there are differences among different buffer zones. Therefore, small-scale urban ecological pattern transformation can enhance the buffer effect of water body and alleviate the urban heat Island effect.