Abstract: The litter decomposition processes by microorganism influenced the carbon sequestration and stabilization. Since tree species, methodology and the length of investigation time are different, three different response patterns of litter decomposition to the global increasing nitrogen deposition had been reported: promotion, suppression and no effect. The mechanisms of litter decomposition affected by nitrogen deposition might be as follows: ① The influences of nitrogen deposition in different concentration on the decomposition of cellulose differed from that of lignin. Because fungi and bacteria have a large biomass and high activity under the low concentration of nitrogen deposition, the opposite response occurs under the high concentration. However, nitrogen deposition promoted decomposition of litters which contained lower portion of lignin and restraint, the higher one according to previous researches.② There is no uniform mechanism of nitrogen deposition affecting extracellular enzyme. Therefore, the rates of litter decomposition responded differently in nitrogen deposition.③The decomposing process of cellulose and lignin in litters would be affected by increasing nitrogen deposition through influencing the microbial biomass, diversity, community composition and stoichiometry, etc.