Artificial thermal environment formed in urban area attract attention in both developed and developing country. Such artificial thermal environment significantly increase discomfort in temperate to tropical cities in summer. Mountain city like Chongqing, China tends to receive severe impact of such thermal effect of human being, it is a typical mountain mega city in which summer temperature rises up to 40℃. This paper is aimed at analyzing thermal environment in mountain city and proposing appropriate urban planning for environmentally sound city, mainly study about building to district scale thermal environment by computer simulation and urban planning for realizing environmentally sound city. Modern computer technique and the computational fluid dynamics technique are used for this research. Impact of slopes, water, city highway, greenbelt, building cluster and other special geography conditions on hot and wet environment in Chongqing is studied.