Water–Ecology–Economy Matching and Coupling Coordination in the Receiving Area of the Chao’er River to West Liao River Water Diversion Project

The national water network is a component of China’s infrastructure, and coordinating ecological security with economic development is important for its construction. Taking the Chao’er River to West Liao River Water Diversion Project, part of the three-horizontal and three-vertical Inner Mongolia water network, as a case study, this paper analyzes the main receiving areas, Tongliao and Xing’an League. Using panel data from 2019–2025, a matching degree model incorporating water resource, ecological, and economic dimensions was constructed. The Gini coefficient and coupling coordination degree were combined to assess spatial matching and its evolution, and improvement pathways for current water allocation are proposed. Water–economy and economy–ecology bivariate matching was generally good, while water–ecology matching remained low, a common weakness in both jurisdictions. Trivariate matching shifted from severe disorder through near disorder toward marginal coordination, with spatial differences: Tongliao showed low-level, strongly fluctuating matching, whereas Xing’an was stable but structurally imbalanced, constrained by a low comprehensive evaluation index. Differentiated pathways are proposed, including strengthened emergency ecological water replenishment in Tongliao and rebalancing the three subsystems, especially improving water use efficiency in Xing’an. These findings support project optimization and water network construction in comparable pastoral areas.