Soil salinization is a main obstacle factor restricting farmland fertility. In order to explore the coupling effect of salt dynamics and soil organic carbon (SOC) accumulation in salinized farmlands under straw returning and screen out the best straw returning amount, the salinized soil of Tumochuan in Inner Mongolia was taken as the research object, six different amounts of straw returning treatments were set up: 0 (CK), 2 100 (ST1), 4 200 (ST2), 6 300 (ST3), 8 400 (ST4), 10 500 kg/hm² (ST5). The dynamic changes of soil salinity and SOC before and after irrigation and the coupling relationship between them were analyzed. The results showed that: 1) Long term straw returning increased SOC content in the 0-30 cm soil layer, with an average increase of 10.0%-35.3% compared to CK. Irrigation also significantly affected the distribution of SOC. After irrigation, SOC content decreased in the 0-30 cm soil layer while increased in the 60-90 cm soil layer (P<0.05). 2) Adding straw effectively reduced soil salinity. Different rates of straw returning significantly reduced the content of water-soluble anions in each soil layer, especially in the 30-60 cm soil layer, HCO₃^-content under straw returning treatments were 85.2%-96.7% lower than that under CK (P<0.05), but the content of water-soluble Ca²⁺increased significantly. After irrigation, salt ion contents gradually decreased with the increase of soil depth, and the cation exchange capacity increased in all soil layers. In conclusion, straw returning is beneficial to carbon sequestration and salt reduction, with the best effect under straw returning rates of 8 400 kg/hm² (ST4) and 10 500 kg/hm² (ST5). It is worth noting that although irrigation can promote the leaching of salt ions, it also can significantly change SOC distribution in different soil layers. Therefore, the effects of irrigation on salt transport and organic carbon accumulation should be comprehensively considered in the practice of saline-alkali soil improvement.