Abstract: The structural characteristics of river system and complex geomorphic environment in the upper reaches of Minjiang River construct the unique water ecology and water environment foundation in mountainous areas, thus shaping the special distribution law of watershed settlements. The study analyzed the plane shape, vertical change, type distribution and spatial differentiation of settlement distribution in the upper reaches of Minjiang River through the adjacent distance of the river, the altitude change of river profile, the grade of catchment basin and the complexity of river system development. The geographic detector is used to reveal the mechanism of hydrological environment coupling geomorphic characteristics affecting the distribution of settlements in mountainous areas in the upper reaches of Minjiang River. The results are as follows: (1) the settlement has the characteristics of “linear” distribution attached to the main river; In general, the number of settlements decreases with the increase of the elevation of Minjiang River tributaries, but there are some differences in different tributaries. The settlements along the main stream of Minjiang River show “U-shaped” distribution characteristics with the increase of river profile altitude. The settlements are concentrated on both sides of the river at an altitude of 873-1 588 m and 1 877-3 369 m; The distribution of settlements of different ethnic groups has obvious catchment level directivity. For example, only Tibetan settlements are distributed in level 1 catchment area, while almost all Han settlements are distributed in level 10 catchment area; The overall settlement density increases with the increase of fractal dimension of watershed water system, and has different spatial differentiation laws in different tributary watersheds. (2) The geographic detector shows that the density of river water system, fractal dimension of water system, altitude and topographic relief are the main control factors affecting the settlement distribution in the upper reaches of Minjiang River, and have significant nonlinear interactive enhancement effect. (3) Through the discussion of terrace development, disaster risk, climate environment and geomorphic landscape characteristics, it is revealed that the production and living environment formed by the coupling of hydrological characteristics and geomorphic environment in the upper reaches of Minjiang River is adaptively selected and utilized by the basin residents, thus forming the internal mechanism of river water system affecting settlement distribution.