Soil water-holding capacity is the major part of forest water storage. Although extensive studies on forest water-holding capacity at plot or slope scales have been conducted, there remains a lack of effective approaches to extrapolate the forest water-holding capacity from plot to watershed scale due to the spatial heterogeneity of environmental factors especially in subalpine watersheds. Here, we used the Zagunao watershed in the western Sichuan as an example to construct the multivariable linear regression models for upscaling soil water-holding capacity from plot to watershed scales based on vegetation and environmental factors by integrating field experiments at a variety of forest types and remote sensing data at a watershed scale, which eventually enabled a rapid evaluation and spatial prediction of soil water-holding capacity at watershed scale. The forest plot level result showed that the water-holding capacity of natural forest was better than that of the artificial forest with the mixed forests better than monoculture. The correlation analysis suggested that soil water-holding capacity was jointly affected by climate, vegetation, soil, and topography such as wind speed, Normalized Difference Vegetation Index (NDVI), and forest age. The upscaling models of the maximum soil water-holding capacity, capillary water-holding capacity and noncapillary water-holding capacity established based on vegetation and environment factors had good performance with the R² of 0.700, 0.720, and 0.908, respectively. The correlation coefficients and mean relative errors based on observations and predictions of the maximum soil water-holding capacity, capillary water-holding capacity and noncapillary water-holding capacity models were between 0.69 and 0.79, and below 20%, respectively, which indicated the good reliability of the models. By use of the upscaling models, the spatial distributions of forest soil water-holding capacity at the watershed scale were estimated. As suggested by the model prediction, the spatial variations of forest soil water-holding capacity are distinct in the Zagunao watershed, where forests at higher elevations are featured with the highest soil water-holding capacity, followed by forests located at a certain distance from roads and rivers in the lower slopes, and the downstream arid valley area has the lowest soil water-holding capacity. The findings can provide effectively scientific supports and assessment tools for the improvement and restoration of ecological functions in subalpine forests.