Based on a long-term (20 years) observation in typical grassland of China West, we analyzed the changing progress of litter accumulation, decomposition and variation of soil water in enclosed grassland. The results showed that exponential equation was adapted to changing trends of accumulation quantity and thickness of litter in grassland communities of Stipa bungeana, Thymus mongolicus, Artemisia sacrorum and S. grandis, the relativities of which werevery distinct in the whole growth period. With air temperature increasing and rainfall enhancing, the litter decomposition speed accelerated. S. bungeana and S. grandis communities needed 150 days to reach to peak value, while T． mongolicus communities needed 180 days and A. sacrorum communities 210 days. There was a strong function of water absorption and retention, which could catch a lot of rainwater and keep soil water seeping in a slow speed. In the nature condition, Soil water saturated content in the growth prophase and anaphase of plant in the S. bungeana, T. mongolicus and A. sacrorum community were was 112.30%～124.02%, 116.61%～134.09%,124.76%～144.32%,respectively. It was favorable to grassland renewal and litter accumulation with 11-15 enclosed years appropriately.