Abstract: Most of the theoretical and practical research on metropolitan integration focuses on large-scale spaces, and there is relatively little research on the collaborative development of small and medium-sized cities in specific regions. This paper aims to explore the phenomenon of metropolitan integration among small and mediumsized cities in the Anning River Valley, Liangshan Yi Autonomous Prefecture, Sichuan Province. Firstly, it sorts out relevant theories such as the conceptual connotation, stage characteristics, and spatial forms of metropolitan integration, and summarizes the cases of collaborative development in river valley areas at home and abroad. The study finds that the Xichang-Dechang-Mianning-Xide region（short for XDMX region） is in the transition stage from the embryonic period to the growth period of metropolitan integration. Considering the problems that Dechang County faces in the process of integrating into the metropolitan integration development of the XDMX region, such as the difficulty in coordinating regional protection and development, weak industrial linkage and mutual promotion, insufficient support from the transportation system, unbalanced allocation of public service facilities, and imperfect collaborative protection mechanism, this paper focuses on the perspective of ’integration of Xichang and Dechang’, constructs a spatial pattern of continuous multi-cluster development in the river valley area. Problem-oriented, it formulates the collaborative development strategies of Dechang County from six aspects: spatial integration, industrial cooperation, transportation interconnection, facility co-construction, ecological co-governance, and service convergence, providing technical support for its integration into regional metropolitan integration and also offering reference for the collaborative development of other different types of small and medium-sized cities.