In order to explore the effects of different straw returning methods on microbial biomass carbon, nitrogen, phosphorus and soluble organic matter under rape/corn rotation system, field experiments were conducted on the purple soil, which was widely distributed in southwestern hilly region of China. This study was expected to contribute to the comprehensive and rational utilization of straw. The results showed that straw directly returning (CS), biochar returning (BC), straw with transformation promoter returning (CSD), equivalent straw and biochar returning (CSB) could all effectively increase the contents of soil microbial biomass carbon, nitrogen and phosphorus. The contents of soil microbial biomass carbon and phosphorus in CSD treatment were the highest, which were 46.32% and 94.09% higher than CK (single chemical fertilizer). Microbial biomass nitrogen content in CSB treatment was the highest followed by CSD treatment, which reached 104.47 mg/kg and 104.14 mg/kg, respectively. Except BC treatment, other treatments improved soluble organic carbon content by 63.26% · 189.46%, and the value of CSD treatment was most distinct, reaching 72.74 mg/kg. Four straw returning treatments decreased the content of soil soluble organic nitrogen (DON) comparing with CK, while the content of soil soluble organic phosphorus (DOP) increased, especially CSD treatment had the best effect on the improvement of soil soluble organic phosphorus. Compared with CK, straw returning reduced the DON/TN, but effectively increased the SMBC/SOC (except BC treatment), CS and CSD treatments had more expressive performance. DOC/SOC and SMBN/TN in CSD treatment were the highest, which reached 0.49% and 7.66%, respectively. Compared with CK, all straw returning treatments could increase the yields of rape and maize by 3.37% ~ 7.01% and 1.49% ~ 3.92%, respectively. CSD treatment was the best among four treatments. The best straw returning method under rape/corn rotation system in purple soil of southwestern hilly region was straw with transformation promoter returning, which had the highest active organic matter and was beneficial to increase soil productivity.