The restriction of topographical height difference in mountain cities results in the poor connectivity and the fragmented open space. Because of the topography and geology, the frequency of secondary disasters is high. Aiming at the characteristic of spatial layout in mountain cities, it analyzes the elements of open space for disaster prevention and preliminarily classifies each element. Comprehensively exploring the influencing factor of disaster prevention space layout in mountain cities, it proposes the differences of composition and evaluation criteria in open space for disaster prevention in mountain cities. It takes the Changshou district as an example, and puts forward the optimization strategies of open space for disaster prevention in mountain cities and the evaluation criteria fitting for the characteristic of mountain cities. It is expected that it will provide theoretical references for further open space planning of disaster prevention in mountain cities.