Southwest mountain cities are characterized by the complex topography, city construction land shortage,and large population and so on.Restricted by physiographic condition,the high density development mode is formed.Based on the concept of high density city,this paper analyzes the high density development characteristics of southwest mountain cities and the reasons for its formation.In the context of the high-density development of southwest mountain cities,this paper analyzes the influence of city scale, density,functional layout and other factors on the transport system,and the influence of transportation means, accessibility and facilities and other factors on the urban spatial structure. And on this basis, the paper puts forward the interactive mechanism between the urban spatial structure and the transportation system in southwest high-density mountain cities,and attempts to reveal the development law of high density city.