In view of low wheat yield and low soil fertility in the dry farmland of Loess Plateau, a study was carried out in a long-term localized experimental field in Lijiabao Town, near Dingxi, to study the effect of biochar (B) and straw (S) addition under three nitrogen levels (no nitrogen application, nitrogen application 50 kg/hm², nitrogen application 100 kg/hm²) (9 treatments in total) on soil organic carbon (SOC) and activated organic carbon in the middle Gansu region of Loess Plateau with the purpose of improving soil fertility and maintaining stable and increased yield. The results showed that compared with no nitrogen fertilizer (CNO), the other fertilization levels could all significantly increase the SOC content, and the effect of BN100 was the most significant as BN100 increased 84.7%, 69.3% and 47.8% of the SOC content in 0-5, 5-10 and 10-30 cm soil layers. The increase of the SOC content by BN0, BN50, and BN100 was significantly better than that of SN0, SN50, SN100, CN0, CN50, and CN100. Compared with SOC, the effect of SN100 on various active organic carbons (MBC, EOC, DOC, and HWOC) was the most significant, and significantly higher than that of CN0, CN50, and CN100. The effects of each treatment on the SOC content and its components showed identical trend as decreased with increment of soil depth. Compared with application of only nitrogen fertilizer, the correlations between SOC and its components were more significant in the treatments received biochar and straw. Addition of biochar showed more significant improvement of the SOC content, and straw addition showed more significant improvement of the soil active organic carbon content. Therefore, the results are of great significance to the improvement of soil microbial environment, the enhancement of soil fertility, the reduction of soil nutrient leaching, and the promotion of crop yield.