Abstract: Salinization-alkalization poses a significant regional eco-environmental challenge to agriculture in Northeast China, making plant diversity essential for ecosystem stability. This study focused on Taonan City, a representative saline-alkali area in the western Songnen Plain. Vegetation survey plots were established to assess plant community composition in both saline-alkali land and grassland. Soil samples were taken from depths of 0-20 cm, 20-40 cm, and 40-60 cm in both land types, and analyzed for pH, total salinity, total carbon, total potassium, total phosphorus, total nitrogen, and ion concentrations. Principal component analysis (PCA) and redundancy analysis (RDA) were applied to explore soil salinization-alkalization characteristics, changes in plant diversity, and their relationships with soil environmental factors. The results showed that Ca²⁺ had the highest proportion among the soil cations in the study area, accounting for 75.76% in saline-alkali land and 75.36% in grassland. \mathrmHCO_3^- was the dominant soil anion, accounting for 57.81% in saline-alkali land and 57.54% in grassland. The main salinization-alkalization factors in this area included K⁺, Ca²⁺, Na⁺, pH, sodium adsorption ratio (SAR), \mathrmSO_4^2- , Mg²⁺ and exchangeable sodium percentage (ESP). The saline-alkali land was classified as a mildly salinized-alkalized soil type, whereas the grassland exhibited strongly alkaline properties but slight salinization without alkalization. Besides, the grassland exhibited greater plant species richness but a significantly lower evenness index compared to saline-alkali land （p<0.05). Total carbon correlated positively with all diversity indices in both land types, while ESP and total potassium showed negative correlations with these diversity indices. This study provides important theoretical insights for managing saline-alkali land and restoring grassland vegetation diversity.