The effects of corn straw returning to the field on microbial biomass，enzyme activity of peanut soil under continuous cropping for 5 years and peanut yield were studied by field experiment. The results showed that the microbial biomass and enzyme activity of peanut continuous cropping soil were significantly increased under different amount of straw addition. The contents of carbon，nitrogen and phosphorus in soil microbial biomass were increased by 12.69% ～ 21.01%，9.66% ～ 25.05%，12.98% ～ 29.08% compared with the control. The soil enzyme activity of urease， sucrase，phosphatase，catalase，lipase and protease were increased by 15.85% ～ 32.46%，17.89% ～ 36.59%， 20.23% ～ 33.16%，26.56% ～ 33.80%，20.54% ～ 32.57%，21.74% ～ 35.36%，respectively. The yield of peanut under the condition of straw returning to the field was 4.49% ～ 10.83% higher than that of the control. The results of correlation analysis showed that soil microbial biomass carbon，nitrogen and phosphorus were extremely significantly correlated with the activities of six enzymes and peanut yield. The above results showed that the addition of corn straw to the continuous cropping peanut soil could effectively improve the soil ecological environment，alleviate the obstacles of continuous cropping，and realize the increase of peanut yield and income.