Assessment of ecosystem service and ecological sensitivity are the basic methods to zone the ecological redline. However, for mountainous areas with complex geological conditions, the indicator system with ecological environment and service as the core is difficult to reflect the impact of a special geological environment, which makes the ecological redline pattern lack support of the geological and geographical process. Based on the mutual feedback of geological environment and geographical environment, this study constructed the vulnerability assessment index system of the eco-geo environment in the southwest mountainous area, Sichuan Province. The ecological redline optimization method was analyzed by superposition with the assessing the frailty, based on the concept of "eco-geo environment community". The results showed that the ecological redline and vulnerability assessment pattern was generally consistent. The vulnerable area of eco-geo environment was 189700 km², accounting for 39.1% of the research area. The total area of the ecological redline was 148000 km², accounting for 30.45% of the research area. Geological and geographical processes in mountainous areas were key factors to shape the distribution pattern of ecological redline. Two redline optimization methods based on the vulnerability assessment of the eco-geo environment, covered an area of 197600 km² and 241700 km² respectively, which was consistent with the ecological security pattern of four key ecological functional areas in the main functional divisions of Sichuan Province. The two schemes reflect the priority protection of the ecosystem and the development and protection pattern of land space, but it should reserve the living space and production space reasonably.