In order to compare the effects of different straw returning rates on soil total organic carbon, microbial biomass carbon, cellulase activity and catalase activity at different soil depths, an in-situ experiment was conducted in a separate mode of planting and returning. The experiment was conducted with four levels of returning amount, i.e. 0% (R0), 0.44% (R1), 0.88% (R2) and 1.32% (R3), and three different returning depths, i.e. 0—15 , 15—30, and 30—45 cm. The result showed that returning for 1 year, soil organic carbon content, microbial biomass carbon content, cellulase activity and catalase activity in 0—15 cm soil layer increased with the increasing amount of straw, and those under R3 treatment had the greatest significantce, which increased by 30.98%, 101.16%, 172.72%, and 5.40%, respectively. In 15-30 cm soil layer, the contents of total organic carbon,microbial biomass carbon and catalase activity in soil treated with straw were higher than those in R0, but there were no significant differences between R1, R2, R3, while cellulase activity increased with the amount of straw returning. In 30—45 cm soil layer, soil organic carbon content, microbial biomass carbon content and cellulase activity of R2 and R3 were significantly higher than those of other treatments, and no significant differences were in catalase activity of all treatment. Compared with returning for 1 year, , the total organic carbon content, soil microbial biomass carbon and cellulase activity during returning for 2 years decreased, with the deree of 8.59%～35.36%, 6.74%～29.16%, and 6.18%～31.72%, but catalase activity increased, the largest increase occured in R3 (with the increase of soil depth, the increase rate of 14.14%, 10.14%, and 12.11%). This study indicates that in the case of separate mode of planting and returning, the high amount of straw can be returned to the field, and also the soil fertility can be improved effectively.