The decline of cities is a complicated process and a sign that the city is at the turning point from flourish to decadence in its developing circle. Due to the diversity of regional factors and predisposing factors, the characteristics, forms and effects of the declined cities are unique. At present, researches in China on decline of cities are mainly concentrated on the macro level and still in the initial stage. First of all, this paper undertakes a summary of the findings from researches on the decline of cities. The paper then chooses the mountainous city which is full of distinctive features as the research object, and analyzes the recession phenomenon of mountainous city in the aspects of the geological and ecological changes, and then discusses the inner mechanism of this phenomenon, in order to figure out some repair methods for declined mountainous cities of this kind, hopping to provide reference for mountainous cities when dealing with the problems such as the geological and ecological changes and decline.