Abstract: Soil salinization represents a critical constraint to global agricultural sustainability, directly inhibiting crop growth and compromising soil ecosystem stability. While substantial research has examined the isolated effects of salt stress on either crops or soil properties, the mechanistic pathways through which salinity influences soil biological barriers via modulation of benzoxazinoid (BXs) metabolism in the maize rhizosphere remain poorly characterized. This study investigated maize rhizosphere soils from three distinct regions of the North China Plain — Cangzhou, Dongying, and Handan — employing an integrated approach combining field surveys with laboratory analyses to systematically examine how soil salinity regulates BXs metabolism and shapes the structure of fungal and nematode communities, while elucidating interactions between pathogenic fungi and herbivorous nematodes under salt stress conditions. Comprehensive analytical methodologies were applied, including high-throughput sequencing targeting the fungal ITS region and nematode 18S rRNA gene to characterize microbial community composition. Major BXs components—DIMBOA, MBOA, DIBOA, and HBOA—were quantitatively analyzed using high-performance liquid chromatography (HPLC). Concurrently, key soil physicochemical parameters, including electrical conductivity (EC) and soluble salt content (SSC), were determined. We employed multivariate statistical approaches including Mantel tests, Pearson correlation analysis, and one-way ANOVA to evaluate complex relationships among salinity parameters, BXs concentrations, and biological community structures. Our findings revealed significant disparities in α- and β-diversity and community composition of both fungal and nematode assemblages across the three regions. Mantel analysis identified soil salinity and BXs composition as primary drivers of these differences, with soluble salt content and electrical conductivity showing significant correlations with fungal communities, while DIMBOA emerged as a key determinant for nematode community variation. Functional annotation of communities demonstrated that Fusarium represented the dominant pathogenic fungal genus across all sites, while all four functional groups of herbivorous nematodes were consistently present. Correlation analyses focusing on plant pathogenic fungi, herbivorous nematodes, soil BXs content, and salinity indicators revealed significant relationships: salinity parameters (EC and SSC) showed substantial correlations with BXs concentrations, with DIMBOA exhibiting a positive correlation with soil salinity while MBOA demonstrated a negative correlation. Further investigation established strong connections between BXs levels and key indicators of soil biological barriers: DIMBOA displayed positive correlations with ectoparasitic herbivorous nematode abundance but negative correlations with the pathogenic fungus Penicillium, whereas MBOA exhibited inverse relationships with these organisms. Crucially, we identified a significant positive correlation between the abundance and infection rates of the pathogenic fungus Fusarium and herbivorous nematodes, suggesting potential synergistic interactions that collectively exacerbate soil biological barriers in saline environments. This study elucidates, from the perspective of rhizosphere metabolite-microbe interaction networks, that soil salinity stress alters the synthesis and accumulation patterns of benzoxazinoids (BXs) in maize, thereby influencing the assembly of rhizosphere fungal and nematode communities and promoting synergistic effects between pathogenic fungi and herbivorous nematodes, ultimately exacerbating soil biological barriers. The synergistic effects among these soil biological barrier factors may further exacerbate crop disease incidence, posing a potential threat to crop production. This research provides novel insights for understanding the crop-soil-microbe interactions in salinized farmland and offers a theoretical foundation for developing ecological strategies to mitigate soil biological barriers in maize cropping systems.