In order to explore the influence of soil microbial biomass by nitrogen deposition in steppe, the way of stimulated nitrogen deposition was applied to treat with plots via N, the influence of cutting on soil microbial biomass C and N at different N-treated levels was researched. The results showed that different N-treated levels didn’t have significant influences on soil microbial biomass C and N, but had the trend of improve soil microbial biomass C and N; interaction of cutting and N-treated decreased soil microbial biomass C and N. Different N-treated levels could decrease roots weight of grassland vegetation, promote soil acidification. The constraint to soil microbial biomass C and N was the best under N-treated of 20g N?m-2?a-1.