【Objective】 In recent years, due to improper use of nitrogen fertilizer, a large accumulation of nitrate in the soil has seriously threatened the soil ecological security of the apple orchard in the loess area. The input of dissolved organic carbon (Dissolved organic carbon, DOC) and intercropping with deep-rooted leguminous crops may be a potentially feasible way to reduce nitrate in the deep soil of the apple orchard, However, research on the feasibility of this approach its effectiveness and influencing factors is currently weak. 【Method】 Therefore, this study set up four treatments in the apple orchard in the northern loess area of Wei River: DOC solution irrigation (D), alfalfa intercropping (M), DOC solution irrigation + alfalfa intercropping (D+M), and control (CK). Various indicators such as nitrate nitrogen, DOC, soil organic carbon (Soil organic carbon, SOC), moisture content, and denitrifying microbial abundance in the 0-600 cm soil layers were measured. 【Result】 The study found that under the D and D+M treatments, the reduction rate of nitrate nitrogen in the 0-400 cm soil profile reached around 50%, but the effect of the single M treatment was not significant. The carbon-to-nitrogen consumption ratio between consumed DOC and nitrate was about 5: 1 in the D treatment, and about 4.35: 1 in the D+M treatment. Both the D and D+M treatments increased the copy numbers of nirS, nirK, and nosZ denitrification genes in the 0-600 cm soil layers, and enhanced the contribution of DOC, SOC, and denitrifying microbes to nitrate reduction.【Conclusion】 Overall, the D+M treatment showed the best nitrate reduction effect and can be considered a feasible measure for controlling deep soil nitrate in orchards in the loess area.