AbstractUrbanization and the ecological resource environment are mutually influential and interdependent, and their coordinated development is the key to the sustainable development of urbanization. Based on a coupling degree model, decision tree, and grey correlation model, the spatial and temporal evolution of the coupling and coordination relationship between urbanization and the ecological resource environment in Southwest China from 2000 to 2018 and its main influencing factors are studied in depth. The thresholds are extracted by the Classification and Regression Tree (CART) to avoid low-coupling coordination. The study finds that (1) the coupling coordination between urbanization and the ecological resource environment in this region shows stagewise development with regional differences. By 2018, except Xizang, all other provinces had entered a high coordination period. (2) The general trend is that urbanization development is on the rise, and the ecological resource environment is fluctuating. The influence of the ecological resource environment subsystem on coordinated development is greater than the influence of the urbanization subsystem. (3) The green coverage of built-up areas is the most important attribute affecting coordinated development. Urbanization still has room for development. The main issues that need to be addressed are population urbanization and social urbanization. Based on the research results, policy recommendations are made to provide a scientific basis for sustainable development and a reference for the formulation of regional new-type urbanization policies.