Regionalization of the urban thermal environment is the technical basis for alleviating the conflict between urban socioeconomic development and the thermal environment based on partition management. In this paper, we constructed a regionalization model for the urban thermal environment. (1) Moderate Resolution Imaging Spectroradiometer land surface temperature products from four seasons were standardized and classified for characterizing the spatiotemporal pattern of the urban thermal environment in 2008. (2) A comprehensive evaluation system of the urban thermal environment was constructed and the principal components were identified by using the spatial principal component analysis method. (3) A self-organizing mapping neural network was used for spatial regionalization of the urban thermal environment. The results show that the distribution levels of the urban heat island are clearer during the nighttime than during the daytime and the high-temperature zone has the higher aggregation degree in summer than in the other seasons. The composition of the underlying surface directly affects the urban thermal environment. The principal components affecting the urban thermal environment include vegetation coverage, geomorphology, urban construction scale, and anthropogenic heat emission. The Beijing metropolitan area was divided into seven urban thermal environment zones, and specific measures and suggestions were proposed for improving the urban thermal environment based on the multiple formation mechanisms of the urban thermal environment in each zone.