Abstract: In western mountainous regions, active tectonics, steep terrain, frequent hazards, variable climate, and fragile ecosystems render suitable spoil disposal sites scarce under multi-factor coupling, making site selection highly challenging. To address the practical challenges of large-scale transportation projects in western mountains characterized by substantial and spatially dispersed spoil volumes and difficult site selection, this study systematically identifies key siting challenges and screens critical influencing factors, proposing a hierarchical multi-factor coupled siting framework comprising extent delineation, site screening, and suitability zoning. A risk-based safety suitability model is developed to quantify the site safety of spoil disposal areas and the potential losses from secondary hazards; an economic suitability model centered on transport costs integrates haul distance and access conditions; and an ecological suitability model uses ecosystem vulnerability as a proxy, assessed across pattern, quality, and service dimensions. Entropy weighting and the Analytic Hierarchy Process (AHP) are combined to derive composite weights, yielding integrated suitability zoning and prioritized candidate site lists. This research provides an efficient, quantitative, and generalizable methodological framework for spoil disposal siting in complex mountainous transportation projects, substantially enhancing siting rigor while minimizing safety risks, disposal costs, and ecological restoration complexity at the source.