In view of the problems existing in the construction of mountainous cities, such as large-scale excavation and construction, large-scale artificial axes and so on, which do not respect the original terrain environment of mountainous areas, this paper proposes adaptability theory into the site design of mountainous cities, so as to form an adaptive strategy for the site design of mountainous cities. From three aspects of the overall balance of excavation and filling at macro level, the coupling subdivision of meso-level platform and the diversified grounding of micro-level buildings, the strategy determines that in the field of site treatment in mountainous cities, attention should be paid to the division of excavation and filling areas, earthwork calculation, platform proportion control, edge line division and height difference elimination of building grounding. Relevant cases prove that the site design guided by this strategy is helpful to form the urban morphological characteristics and spatial environment with mountain characteristics. This strategy is a site design method which conforms to the topographic characteristics and construction laws of mountain cities. It can improve the relevant planning and design theory and guide the construction practice of mountain cities.