Some settlements were located in unsuitable regions due to limited land resources in mountainous areas, some settlements were even even constructed in areas prone to geological hazards in Southwest China. Therefore, it was important to evaluate the spatial appropriateness of a region and determine the areas that were unsuitable for settlements, and then find out the settlements located in unsuitable regions. It will assist in decision making associated with the relocation of settlements. Furthermore, it will be the key to ensure the safety of inhabitants and promoting sustainable development in mountainous areas. This study explored the coupling mechanism between suitable space and rural settlements in the upper Minjiang River basin, which is an ecologically fragile area with high-frequency of natural hazards. Firstly, we identified relief degree of land surface (RDLS), elevation, and disaster risk as the limiting factors. Then, by determining the thresholds of these limiting factors, we recognized the suitable areas for inhabitation in the upper Minjiang River basin with GIS. Finally, using the distribution map of rural settlements and that of suitable space, the distribution of rural settlements located at unsuitable area was obtained by coupling relationship analysis. Consequently, an in-depth understanding of this relationship was achieved as follows: (1) The suitable space of the upper Minjiang River basin is 13.7 thousand km(2), accounting for 54.9% of the total land space; (2) There were 196 settlements located in the unsuitable area, the total area of these settlements was 125.27 km(2), and there were 68000 people in these settlements, accounting for 17.65% of the total population; (3) There were 65 settlements located near mountain hazard areas, accounting for 4.9% of the total. These findings suggest that it was necessary to carefully investigate settlements with risks and develop targeted relocation policies to help find the most effective way of using land safely and to good effect. The details are as follows: (1) Fully consider the safety of residents: For the 196 settlements distributed in the unsuitable region, the government should undertake a point-by-point survey and classify these settlements into different categories for relocation; (2) For the 65 settlements closely related with mountain hazards, professional geological prospecting teams should be organized to conduct a field survey at each point; (3) Besides considering the safety of residents during the relocation process, it is necessary to pay more attention to the cultural customs of inhabitants and livelihood sustainability
