Analyzing the characteristics of soil carbon and nitrogen hydrolase activity and microbial population structure in rice-rape rotation farmland in Erhai watershed, providing a basis for optimizing the structure of farmland soil microbial community and regulating community functions, and realizing the optimal management and reasonable protection of farmland ecosystem. Two experimental treatments without applying any organic carbon source and chemical fertilizer and applying chemical fertilizer without applying organic carbon source were selected as the research objects, and the soil β-1，4-glucosidaseactivity(GC)，β-1，4-N-acetyl glucosidaseactivity(NAG) and microbial population composition were analyzed in two treatments with long-term application of nitrogen and no application of nitrogen.The results showed that the activity of soil β-1，4-glucosidase was positively correlated with soil organic matter，and the activity of soil β-1，4-N-acetylglucosidase was positively correlated with total nitrogen and analyze the relationship between soil enzyme activity, microbial population and soil carbon and nitrogen.Soil carbon nitrogen ratio(C/N)was the main environmental factor that affected the activity of hydrolase.The main populations of soil bacteria were Proteobacteria(32.58%～34.43%)，Acidobacteria(20.19%～22.38%)，Chloroflexi(15.39%～18.53%)，Actinobacteria(14.91%～18.58%)and Gemmatimonades(3.39%～4.21%)，which accounted for 91.54%～93.10% of the total prokaryotic community.The main populations of soil fungi were Ascomycota(76.75%～78.39%)，Basidiomycota(8.91%～11.54%)and Zygomycota(6.12%～7.49%)，which accounted for 93.26%～96.63% of the total eukaryotic community.The variation of microbial population diversity and abundance of phylum level was not significant(P≥0.05).It showed that long-term application of chemical fertilizer resulted in the change of population abundance of some microbial species with significant difference.Higher carbon and nitrogen content in soil is the main environmental factor to maintain the soil microbial diversity and enzyme activity stability in rice-rape rotation farmland in Erhai basin.