Abstract: In order to reveal the effect of mixed exogenous carbon returning of crop straw and litter leaves on farmland soil quality in black locust-maize agroforestry system in loess hilly region. In this study, based on a 4-year locational trial, the effect of returning straw and litter leaves in different proportions to the field on the soil quality of farmland in the agroforestry complex in the Loess Hilly Region was investigated, with the non-returned treatment as the control (CK). The results show that :① There were differences in soil physical, chemical and biological properties among different soil layers. Compared with CK, Y3C1 and Y1C3 treatments significantly increased soil water content, organic carbon, available phosphorus, nitrate nitrogen and ammonium nitrogen content in 0-20cm soil layer. At the same time, the activities of BG ( β-1,4-glucosidase ), NAG ( N-acetyl-β-glucosaminidase ) and LAP ( leucine aminotranspeptidase ) in this soil layer were also significantly increased, and the activities of the three enzymes were increased by 55.30%-66.35%, 91.41%-101.26%, 24.58%-26.20%, respectively. In the 20-40cm and 40-60cm soil layers, each treatment had little effect on soil properties.② Y4C0, Y3C1, Y2C2, and Y1C3 treatments significantly increased SQI compared to CK, and Y3C1 treatment had the best improvement effect, which was significantly increased by 14.44 % compared with the control. ③ Random forest analysis showed that soil ALP activity, available potassium, nitrate nitrogen and available phosphorus content were the key factors affecting the change of SQI in farmland of agroforestry systems in the Loess Hilly Region. Comprehensive analysis showed that SQI and corn yield were the highest under Y3C1 treatment, and the effect was the best. It can be recommended as a suitable ratio of straw and litter returning to the field to improve the quality of farmland soil in the agroforestry system in this area.