Abstract: Soil organic matter is a fundamental aspect of cultivated land quality, which not only promotes the formation of soil aggregates but also provides nutrients for plants and microorganisms. The formation and decomposition of soil organic matter are inseparable from the participation of microorganisms. Soil aggregates not only provide a habitat for microorganisms but also provide physical protection for organic matter. In soils with high salt content, the accumulation and decomposition of organic matter become more complex. Therefore, this paper summarized soil salinization and its deleterious effects, analyzed the impact of soil salt on soil aggregate structure and microbial characteristics, and described the characteristics and accumulation rules of organic matter in saline-alkali soil. Additionally, the research progress on the impact of soil salt on soil organic matter was summarized to reveal the potential mechanism of carbon sequestration in salt-affected soils. Previous studies have shown that the organic matter content in salt-affected soil is low, the aggregate structure is poor, and the microbial activity is low. Poor soil structure leads to the exposure of soil organic matter and facilitates greater decomposition, and the low amount of exogenous organic matter input leads to difficulty in the accumulation of soil organic matter. It can be seen that salt-affected soil is a potential carbon pool, and appropriate measures can significantly increase the organic matter content of salt-affected soil. On this basis, future research directions for organic matter accumulation in salt-affected soil were proposed: 1) the response of soil aggregate structure and soil microorganisms in the process of organic matter partitioning under different salt environments; 2) the response of soil aggregate structure and soil microorganisms in the process of organic matter accumulation under the addition of exogenous organic materials; and 3) the productivity characteristics of salt-affected soil after the increase in soil organic matter. The above research clarifies the turnover mechanism of organic matter in saline-alkali soil, provides a theoretical basis for “carbon sequestration” of saline-alkali land, and provides targeted measures to improve the quality of saline-alkali farmland and promotes the green sustainable development of saline-alkali land.