[Objective] The evaluation of carrying capacity of territorial space resources and environment in watersheds were studied based on multi scale fusion in order to provide scientific basis and reference for the sustainable development of the basin, and promote the coordinated development of resources and environment. [Methods] Using the Minjiang River basin as an example and considering the multifunctional characteristics and connotations of territorial spatial resources, we established a multi-scale evaluation system for territorial spatial resources and environmental carrying capacity. By applying an improved multiscale integration model, this study conducted a detailed micro-analysis of the evaluation results for research cross-sections from the years 2000, 2010, and 2020. [Results] ① Over the long term, the overall ecological carrying capacity (CC_E) of the basin has mostly been at a medium level. The living carrying capacity (CC_L) has generally been at a medium level or below, while the production carrying capacity (CC_P) has predominantly been at a very low level. Consequently, the comprehensive carrying capacity (CC_C) has mainly been at a low level, with no instances of a very high level. ② During the study period, the regions with low levels of all carrying capacities expanded. The expansion of CC_E mostly occurred in the middle and southeast of the basin; the expansion of CC_L occurred in the upper, middle, and lower reaches of the basin; the expansion of CC_P mostly occurred in the western and southern parts of Shuangliu and Renshou; and the expansion of CC_C mostly occurred in Wenchuan, Pujiang, and Jingyan. ③ The high CC_E and low CC_L and CC_P in the upper reaches of the Minjiang River can be attributed to the combined effects of topographical conditions and socioeconomic levels. In contrast, Chengdu’s central urban area has achieved outstanding levels of CC_L, CC_P, and CC_C, driven by high-quality socioeconomic development, and has maintained these levels over the long term. [Conclusion] The Minjiang River Basin exhibits significant regional differences in natural conditions and socioeconomic levels, resulting in varying levels of carrying capacity across different areas and hindering coordinated and balanced regional development. Persistently promoting high-quality development and leveraging the spillover and radiative effects of Chengdu City, the provincial capital, will help enhance the carrying capacity levels, reduce regional disparities, and drive overall coordinated development across the basin.