Abstract: Five soil profiles with different micro geomorphological units in a typical depression of Songnen Plain were selected by means of field investigation and physical and chemical analysis. The morphological characteristics of soil profile of soda saline soil in this area were studied, and the composition and distribution characteristics of soluble salt were analyzed. The results showed that the distribution trend of alkalinity and total soluble salt in soil profile was similar to that in different micro geomorphology, indicating that the salt accumulation and alkalization in soda saline-alkali soil were synchronous; the soluble salt composition were mainly K⁺ and Na⁺, HCO₃⁻ and CO₃²⁻; the depth of P1 profile 0-60 cm and P3 profile 0-40 cm salt content were large and concentrated, and the salt surface accumulation was significant; the salt content of other profiles showed a trend of high in the middle and decreasing downward; and the soil types of saline-alkali soil from west to east were shallow sodic salinized alkaline soil - white crust sodic salinized alkaline soil-soda light salt weakly alkalized meadow soil-soda weakly alkalized saline soil. The formation of soda alkali soil in multi regions was complex.