Abstract: Alnus formosana-Hemarthria compressa(model A)and A. formosana-natural weed(model B)were chosen as the experimental models in this study. The decomposition bags method was used to explore the characteristics of litter decomposition and dynamics of nutrient release under & over ground. The results were as follows:① Leaves decomposed more fast after one year, followed by fine roots(mixed roots), whereas, branches was the slowest. Moreover, there were significant differences in the dry quality retention rate of leaf, branch, and root(P<0.05), which were significantly lower in model A than that in model B. Results of ANOVA showed that planting H. compressa significantly increased decomposition rate of branches and roots(P<0.05), however, it did not significantly influence the decomposition rate of leaves(P>0.05). ② Original content of lignin, the ratio of m(C)to m(N), m(lignin)to m(N)and m(lignin)to m(P)were negatively correlated with dry litter quality retention rate(P<0.05, P<0.01), respectively. The contents of N were positively correlated with dry litter decomposition rate of those research objects(P<0.05)except fine roots in model B. ③ In process of decomposition of leaves, branches, and roots, C and K statuses were net release, and N status was enrichment-release, whereas, P status was net release rapidly in leaves decomposition. Thus, planting H. compressa significantly speed up the release of C(except leaves), N and P(P<0.05)in the leaves, branches, and roots.