Abstract: Mountain forest in Western Sichuan is an important part of water conservation forests in Southwest of China, and Picea asperata Mast. plantation is one of main types. Clarifying its water conservation capacity and its influencing factors are very important to regional ecological security. In order to explore the effects of forest age on ground cover and soil hydrological function of Picea asperata Mast. plantation in the sub-alpine region of western Sichuan, a comparative study was carried out. The Moss, litter and soil samples of Picea asperata Mast. forest at different ages (20-year-old, 30-year -old and 40-year-old) were investigated and sampled, then the hydrological function of those samples were analyzed. The result showed that (1) tree biomass and shrub coverage increased, but grass coverage decreased with increasing plantation age. Shannon-weiner index of shrub and grass both firstly deceased and then increased. (2) Meanwhile, hydrological function of moss played a dominant role in forest ground cover, and the moss accumulated mass (CM) firstly deceased and then increased, but there were no significant difference on maximum water holding rate (MWHR) and maximum water holding capacity (MWHC). However, MWHR and MWHC of litter increased significantly with forest ages, and maybe this was related to changed light, atmosphere and soil humidity conditions with increasing forest ages. (3) Finally, soil density decreased with increasing forest age, mainly due to the increase of forest biodiversity, shrub coverage and moss accumulation. (4) In summary, community structure of Picea asperata Mast. plantation with 2 300 plants per hectare was gradually complicated, soil texture was gradually improved, and hydrological effects were also enhanced. A long-term study is needed to further investigate the Picea asperata Mast. plantation age effects on hydrological and ecological function.