Plant diversity was crucial for maintaining the stability of wetland ecosystem. This study focused on the Yellow River Delta wetland ecosystem, integrating field observation data with a salinity gradient response model to systematically analyze the spatial variation characteristics of soil environmental factors, the changing patterns of wetland plant diversity, and their interrelationships with soil ecological factors. The results revealed distinct spatial patterns: soil salinity levels were significantly higher in the northern and coastal areas of the study region, while lower salinity levels were predominantly found in the southern and central regions. Soil bulk density exhibited a clear spatial distribution pattern, increasing progressively from the central zone towards the periphery. Total carbon, total nitrogen, and total phosphorus shared a similar spatial trend, all decreasing from the inland areas towards the coastline. High pH zones were primarily distributed in the northwestern and coastal areas. Whereas available phosphorus and potassium showed relatively uniform distributions overall, with their high-value zones concentrated mainly in the southern region. High-value organic carbon zones were mainly distributed in the central and southwestern parts. A key finding was that the plant diversity index of the Yellow River Delta wetlands exhibited a marked decline with increasing soil salinity gradients. Quantitatively, compared to low-salinity gradient, medium-salinity gradient and high-salinity gradient exhibited lower plant richness indices (61.3% and 78.4% reduction, respectively), Shannon-Wiener indices (48.5% and 77.9%), dominance indices (38.6% and 70%), and uniformity indices (26% and 55.8%). This unequivocally demonstrates salinity stress as a primary environmental pressure suppressing wetland plant diversity in this region. The interaction between plant diversity and soil factors exhibited significant response characteristics to salinity gradients, indicating that the dominant regulatory soil factors governing plant diversity varied distinctly across the salinity spectrum. In low-salinity gradient habitats, soil organic carbon, available potassium, and total phosphorus emerged as the dominant regulatory factors. In medium-salinity habitats, total nitrogen and available phosphorus played the primary roles. In high-salinity gradient habitats, total phosphorus became the foremost regulatory factor influencing plant diversity. This shift in dominant factors across gradients highlighted the adaptive adjustments in plant community strategies in response to escalated environmental stress. The findings of this study not only helped to deeply understand of the key soil factors influencing plant diversity under different salinity gradients in the Yellow River Delta and the gradient-dependent mechanisms governing their effects, but also provided a vital scientific reference and decision-making basis for the targeted protection, ecological restoration, and sustainable management of wetland plant diversity and resources in the region.