Mitogen-activated protein kinase (MAPK) cascades are critical for fungal development, stress adaptation. and virulence. However, their dynamic and stress-specific regulatory networks in entomopathogenic fungi remain largely unresolved. This study systematically investigates the roles of all three key MAPKs—BbHog1, BbSlt2, and BbMpk1—in insect pathogenic fungus Beauveria bassiana. A combination of detailed phenotypic profiling of deletion mutants (ΔBbHog1, ΔBbSlt2, and ΔBbMpk1) and time-course transcriptomics (RNA-seq at 0, 0.5, and 12 h) under osmotic, cell-wall, oxidative, and thermal stress conditions was employed, followed by weighted gene co-expression network analysis (WGCNA). This approach delineated twelve stress-responsive gene modules regulated by those MAPKs that were highly associated with fungal stress adaptation, including membrane repair, redox balance, cell-wall remodeling, and core metabolism. Functional analyses showed that Hog1 orchestrates osmoadaptation through coordinated control of osmolyte metabolism, glycolytic flux, and cell-wall remodeling; Slt2 protects against thermal damage by sustaining membrane integrity, ergosterol homeostasis, and redox balance; and Mpk1 directs oxidative stress responses by tuning mitochondrial activity, metabolic suppression, and detoxification pathways. In summary, this work outlines a concise, systems-level framework of MAPK-mediated stress regulation in B. bassiana, providing mechanistic insight into fungal environmental resilience and identifying molecular targets for the engineering of robust biocontrol strains.