Abstract: In order to reveal the influence of groundwater irrigation on the soil carbon(C) cycle on a regional scale, the non-irrigated area, low irrigation area, and high irrigation area in the North China Plain were chosen as the research object in this study. The vertical distribution of C content and changes in C storage from 0 to 700 cm were measured in these areas. Then, the end member model and stable C isotope source analysis technology were used to quantitatively evaluate the contribution of different sources to soil C pools under groundwater irrigation conditions. The results showed that: (1) Groundwater irrigation had no significant effect on soil organic carbon (SOC) storage, but groundwater irrigation significantly increased soil inorganic carbon (SIC) storage in the irrigated area, and it showed an increasing trend with the increase of irrigation volume (43.8, 46.9, 79.9 kg/hm², respectively). In addition, the vertical profiles showed that there was a significant difference in C density between irrigation and non-irrigated areas at a depth of 100-300 cm. (2) According to the result of correlation analysis, the conversion relationship between SOC and SIC was strong under non-irrigated conditions, and relatively weak under irrigation conditions. It could be attributed to the external input of dissolved inorganic carbon (DIC) from groundwater, which became a controlling factor for the soil C pool. (3) Based on stable C isotopes source analysis, SOC mainly came from C3 plants, and SIC of non-irrigated area mainly came from SOC conversion, accounting for 10.6%-25.8%, while irrigation area SIC came from groundwater irrigation and reached 74.0%-89.8%. The results showed that the DIC input from groundwater irrigation significantly increased the SIC storage and had a vital impact on the composition and transformation process of the regional soil C pool.