In order to find a reasonable and efficient mode of carburizing and reduce the loss of organic carbon in alkalized soil, the effect of different organic materials addition on the capacity of dissolved organic carbon in saline-alkali soil of Hetao Irrigation District in Inner Mongolia had been studied. Taking mild and moderate saline-alkali soil in Hetao Irrigation District of Inner Mongolia as the objects to carry out field trials, the three treatments of biochar (BC), goat manure (GM), and CK were used to compare and analyze the changes of soil organic carbon (SOC), dissolved organic carbon (DOC), and soil physio-chemical properties after adding different organic materials. The results showed that: (1) compared with CK, the DOC capacity treated by BC and GM in mild alkalized soil has increased by 3.28% and 20.66%, the SOC capacity has increased by 5.40% and 10.30%, respectively. The capacity of dissolved carbon treated by BC and GM in moderate alkalized soil had increased by 41.32% and 74.10%, and the SOC capacity had increased by 60.24% and 79.16%, respectively. (2) There was a negative correlation between DOC capacity and SOC capacity treated by BC and GM in mild alkalized soil, and a positive correlation between DOC capacity and SOC capacity treated by BC and GM in moderate alkalized soil. (3) The capacity of SOC and DOC in saline-alkali soil was mainly related to the change of soil pH and conductivity, compared with the treatment of GM, the conductivity of BC was about 1.93%~29.15% lower, while the soil pH and alkalinity of GM was 0.31%~1.53% and 7.10%~24.63% lower than that of BC, respectively. In general, the addition of organic materials could increase the capacity of SOC and DOC in the soil, and reduced the degree of soil alkalization, and the addition of GM was slightly better than that of BC. Therefore, compared with BC, GM was more effective to improve the carbon capacity of alkalization soil in Hetao Irrigation District, the effect of soil amendment was better, and the improvement of soil physio-chemical properties was more obvious.