Mountainous regions characterized by complicated terrain are more vulnerable to ecological environments, geologic hazards, and human activities than plains and basins. This paper first measured the eco-geological environment (EGE) of the Three Gorges Reservoir area (TGRA) from 2002 to 2022. Next, it constructed a system for assessing the degree of economic development using the entropy weight method. Lastly, it employed the coupling coordination degree (CCD) model to conduct a thorough analysis of the connection between the quality of the EGE and its economic development. The findings show that: (1) During the previous 20 years, the regions with "good" and "excellent" EGE quality in the TGRA are mainly concentrated in the regions with rugged terrain, while the areas with "poor" and "bad" are primarily focused on the core urban area of Chongqing with flat terrain. (2) From 2002 to 2022, the TGRA's EGE and economy development show a rising trend in relation to the degree of coupling and coordination; their coordination level increased from the stage of slight imbalance to the stage of moderate coordination. (3) The economically developed area has a much greater CCD than the economically backward area, while the flat terrain area has a significantly larger CCD than the steep terrain area. This study establishes a scientific foundation for the prospective attainment of sustainable development in the mountainous region.