This study aimed to evaluate the water conservation function of forestlands in the Western Sichuan Plateau and investigate the water-holding characteristics of the litter and soil layers. Forest lands at low elevation (2050m and 2250m) with Populus simonii and Quercus mongolica, middle elevation (2450m and 2750m) with Pinus massoniana and Corylus avellana, and high elevation (2950m) with Tsuga chinensis in Kangding City, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, were selected as the study objects. The thickness, accumulation, effective retaining content of the forest litter layer and soil layer parameters such as soil bulk density, capillary porosity, saturated water conductivity, and organic carbon content at different elevation gradients were measured and analyzed. Principal Component Analysis (PCA) and fuzzy mathematical membership function methods were applied to evaluate the water conservation ability. The results showed that: (1) At 2750m, the litter layer exhibited significantly greater thickness, accumulation, and effective retention compared to those at 2050m, 2250m, 2450m, and 2950m, with increases of 24.43%, 141.39%, and 17.25%, respectively (P < 0.05). The highest soil non-capillary porosity and surface organic carbon content were observed at 2450m. Specifically, soil organic carbon at this elevation was 147.06%, 71.65%, 36.39%, and 41.55% higher than at 2050m, 2250m, 2750m, and 2950m, respectively. (2) Among the variables analyzed, soil non-capillary water storage, non-capillary porosity, and soil bulk density were the dominant factors affecting forest water conservation functions, followed by the effective retaining content and thickness of the litter layer. These factors interact with each other and jointly affect the water conservation function of forest land. (3) There were significant differences in the water conservation function of forest land s across different elevation gradients (P<0.05), with the highest water conservation ability observed at middle elevations, followed by low elevations, and the lowest at high elevations. The water conservation function of forests at different elevation gradients ranged from 306.20 to 397.01t/hm2. Compared with those at middle elevations, the water conservation function of forests at low and high elevations decreased by 8.95% and 34.63%, respectively. (4) In the 0-30cm soil layer, the water conservation function of the soil layer is significantly higher than that of the litter layer, approximately 12.10 times greater, indicating that the soil layer had a stronger capacity for water retention and regulation. The findings of this study provided scientific support for the protection and restoration of forest ecosystems and the maintenance and enhancement of water conservation functions in the Western Sichuan Plateau.