Woody debris (WD) is the basically structural component in most of forest ecosystems worldwide, and plays crucial roles in holding water, conserving soil, promoting forest regeneration, nursing biodiversity, and modulating the cycles of carbon and nutrients in the forest ecosystem. Generally, WD consists of coarse woody debris (CWD) and fine woody debris (FWD). Among these, CWD provides better substrate for the growth of epiphytic moss. Further, the epiphytic moss on the CWD also plays important roles in holding water, regulating the bioelement cycles, and nursing biodiversity. Together, both WD and its associated epiphytic mosses might exert paramount roles in regulating the hydrological process, in particular holding water in the the forest ecosystem. Although the water-holding characteristics of CWD and moss have been widely investigated in different forest ecosystems, the simultaneous investigation on the water-holding capacity in both WD and its associated epiphytic moss has not been reported. Furthermore, the changes in water-holding capacity of epiphytic moss on CWD with decay classes and diameter sizes are not investigated. The changes in water-holding capacity of WD and its epiphytic moss with forest types, decay classes and diameter classes were therefore investigated in eight typical subalpine forests in western Sichuan. The saturated water-holding capacity of WD varied greatly with forest types, decay classes and diameter sizes. The highest and lowest saturated water-holding capacity of WD were observed in Picea purpurea primary forest (22.06 mm) and willow secondary forest (4.55 mm), respectively, but the ratio of water-holding varied slightly with forest types. Meanwhile, the saturated water-holding capacity of epiphytic mosses on the WD also varied greatly with forest types, and the highest and lowest values of saturated water-holding capacity were found in Picea purpurea primary forest (7.01 mm) and Sabina saltuaria primary forest (0.21 mm), respectively. Moreover, decay classes gave stronger effects on the saturated water-holding capacity of WD, higher and lower values of saturated water-holding capacity of WD were respectively measured on decay class IV (3.77 mm) and decay class II (0.75 mm). Particularly, the saturated water-holding rate of WD and saturated water-holding capacity of epiphytic moss correlated significantly (P<0.05) and positively with WD decay class, which fitted the quadratic term function as Q(Q')=ex²+fx+g. The saturated water-holding capacity of WD and its associated epiphytic mosses on the WD increased with diameter classes, and the saturated water-holding capacities of WD with diameter size>50 cm (D5) and its epiphytic mosses on the D5 WD accounted for 60% and 40% of the total saturated water-holding capacity in the subalpine forest ecosystems in Wanglang National Nature Reserve. In conclusion, these results suggested that forest types, decay degree and diameter sizes of WD were the key factors that determine the water-holding capacity of WD and its epiphytic mosses in the subalpine forest region. Particularly, CWD epiphytic moss plays an important role in improving the water-holding capacity in the subalpine coniferous forest region.