Abstract: Grassland degradation caused by salinization is a common ecological problem in grassland ecosystems of arid and semi-arid regions. Taking the saline-alkali grassland in the western Songnen Plain as the research object and aiming at the vegetation degradation problem under saline-alkali stress, this study examined the characteristics of soil seed bank density and species richness of two typical dominant plant communities, Leymus chinensis and Chloris virgata, under different saline-alkali gradients through field vegetation surveys and greenhouse germination experiments. The relationships among soil seed banks, aboveground vegetation, and soil physical and chemical properties were analyzed. The results show that: (1) The species richness of the seed bank in the Leymus chinensis community has no obvious difference within the range of its distributed salinization gradient, while the seed density decreases significantly from 468 seeds·m^-2 to 130 seeds·m^-2 along the saline-alkali gradient. The species richness and seed density of the soil seed bank in the Chloris virgata community in the plots with the highest salinization degree are significantly lower than those in other plots; specifically, the species richness decreases from 4 to 1, and the seed density ranges from the maximum of 2 078 seeds·m^-2 to the minimum of 13 seeds·m^-2. (2) The two dominant plant communities exhibit different tolerance degrees to saline-alkali conditions. The Leymus chinensis community is distributed in the soil with pH value, electrical conductivity, and alkalization degree ranging from 7.47 to 8.28, 0.16 to 0.43 mS∙cm⁻¹, and 1.52% to 4.97%, respectively. The Chloris virgata community could distribute under higher saline-alkali conditions, with the soil pH value, electrical conductivity, and alkalization degree being 8.66 to 9.72, 0.33 to 1.13 mS∙cm⁻¹, and 9.3% to 48.6%, respectively. (3) The response mechanisms of the soil seed banks of the two plant communities to salinity-alkalinity, nutrients, and aboveground vegetation communities are different. The aboveground vegetation directly affectes the soil seed bank of the Leymus chinensis community; meanwhile, soil saline-alkali conditions indirectly regulates the soil seed bank by affecting soil nutrients. Nutrient conditions and soil saline-alkali status directly affect the characteristics of the soil seed bank of the Chloris virgata community; in addition, soil salinity-alkalinity indirectly regulates the soil seed bank by influencing the aboveground vegetation. This study provides a theoretical basis for the protection and restoration of typical grassland vegetation in saline-alkali stress environments.