In order to study the effects of different doses of sweet potato vine and their biochar returning to the field on microbial activity and nutrient contents of dryland red soil, field positioning experiment was conducted. In the experiment, five treatments were set up, which were conventional management (CK), 3 000 kg/hm² sweet potato vine returning (S1), 6 000 kg/hm² sweet potato vine returning (S2), 1 000 kg/hm² sweet potato vine biochar returning (BC1) and 2 000 kg/hm² sweet potato vine biochar returning (BC2). The results showed that compared with CK, in the 0—10 cm soil layer, soil basal respiration of BC1 increased by 17.93%, while that of S1, S2 and BC2 decreased by 20.33%, 10.10% and 2.66%, respectively. In the 10—20 cm soil layer, the soil basal respiration of S2 and BC1 increased by 17.29% and 0.41%, respectively, while that of S1 and BC2 decreased by 13.61% and 16.93%, respectively. In the 20—30 cm soil layer, the basal respiration of S1, S2, BC1 and BC2 increased by 8.26%, 48.94%, 50.21% and 38.59%, respectively. Compared with CK, the soil microbial biomass carbon of S1, S2, BC1 and BC2 treatment increased about 1.30%, 6.09%, 28.52% and 39.64% in the 0—10 cm soil layer, respectively. In the 10—20 cm soil layer, soil microbial biomass carbon of S1, S2, BC1 and BC2 increased by 9.76%, 16.72%, 24.20% and 54.32%, respectively. In the 20—30 cm soil layer, soil microbial biomass carbon of S1, S2, BC1 and BC2 increased by 22.34%, 39.27%, 54.06% and 84.09%, respectively. It showed that sweet potato vines and their biochar could promote the soil basal respiration and soil microbial biomass carbon content to a certain extent. Sweet potato vine returning promoted the activities of soil FDA hydrolase and soil urease, but had little effect on soil sucrase activity. Returning biochar to the field inhibited the activities of soil FDA hydrolase and soil urease, and promoted soil sucrase activity. Sweet potato vine returning increased the content of soil organic carbon, while biochar returning reduced that. Sweet potato vine and biochar returning both increased the contents of hydrolyzed nitrogen and available phosphorus in the soil. The results showed that the addition of sweet pototo vine and biochar could effectively improve the soil physical and chemical properties and soil microbial activity, which was of great significance to improve the stability of soil ecosystem. The results provided a theoretical basis for the rational return of straw and biomass carbon to the field.