This study was conducted at Ningdong photovoltaic station in Ningxia, China, to investigate the effects of different patterns of sowing mixtures of forage species on soil organic carbon (SOC) and its active fractions. Through natural restoration and mechanical no-tillage mixed sowing techniques, five mixed sowing configurations were established to examine the distribution characteristics and factors influencing SOC and its labile fractions—including easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC)—in both inter-panel and under-panel habitats. The results showed that sowing a mixture of gramineous and leguminous species significantly increased SOC and its active carbon components. Specifically, “a mixture of Astragalus laxmannii+Lespedeza davurica+Astragalus laxmannii+Lespedeza davurica” exhibited the highest SOC, EOC, and MBC contents in the 0-20 cm soil layer between photovoltaic panels, reaching 3.91 g·kg-1, 2.34 mg·kg-1, and 151.30 mg·kg-1, respectively—representing increases of 26.13%, 141.24%, and 167.92% compared with the control (CK). “A mixture of Astragalus laxmannii+Lespedeza davurica+Astragalus laxmannii+Lespedeza davurica + Medicago sativa” performed best beneath the solar panels, with SOC reaching 3.95 g·kg-1 in the 0-20 cm soil layer—63.90% higher than CK—while EOC and MBC reached 1.61 mg·kg-1 and 127.69 mg·kg-1, respectively, significantly surpassing CK and most other patterns. In contrast, the sowing of a single gramineous species exhibited the lowest SOC content in the 0-20 cm soil layer between panels, at only 2.71 g·kg-1 14.39% lower than for CK. It also showed a weaker capacity to accumulate EOC and MBC, although SOC accumulation improved in the soil layer of 20-40 cm in depth. Overall, SOC levels were generally higher between photovoltaic panels than beneath them, while the DOC/SOC ratio was higher beneath the panels, indicating a short-term advantage in carbon supply in these areas. Redundancy and variance partitioning analyses revealed that SOC and its active components were significantly regulated by soil physicochemical properties, including total nitrogen, total phosphorus, available nitrogen, and electrical conductivity, with chemical factors exerting a greater influence than physical ones. In conclusion, the mode of sowing a mixture of Astragalus laxmannii, Lespedeza davurica, Astragalus laxmannii, and Lespedeza davurica demonstrated the best effectiveness in enhancing soil carbon sequestration and carbon pool activity, making it the most suitable option for deployment between photovoltaic panels, whereas sowing a mixture of Astragalus laxmannii, Lespedeza davurica, Astragalus laxmannii, Lespedeza davurica, and Medicago sativa performed optimally beneath the panels. The sowing of a single gramineous species showed relatively weak overall performance, with only some advantages in terms of carbon accumulation in deep soil.