<p>This study investigates the prevalence of occupational stress among metal mining workers in China and its association with depressive symptoms, insomnia, and work-related musculoskeletal disorders (WMSDs), while also exploring insomnia as a potential mediator. A cross-sectional survey of 1130 metal mining workers in China was conducted from June to November 2023. Occupational stress, depressive symptoms, insomnia, and WMSDs were measured using standardized instruments. Due to the high prevalence of the outcomes, Poisson regression models with robust variance were used to estimate adjusted prevalence ratios (RRs). Subgroup and mediation analyses were also performed. Restricted cubic splines were used to flexibly model the dose–response relationship between occupational stress scores and health outcomes. The prevalence of occupational stress was 28.8%. After adjustment, workers with occupational stress had a higher risk of depressive symptoms (RR = 3.24, 95% CI 2.42–4.34), insomnia (RR = 1.47, 95% CI 1.25–1.73), and WMSDs (RR = 1.19, 95% CI 1.10–1.28). Younger workers and those with lower incomes appeared more vulnerable. Insomnia was confirmed as a partial mediator in the relationship between occupational stress and both depressive symptoms and WMSDs. A clear dose–response relationship was observed; spline analysis further revealed a non-linear association for depressive symptoms, with the risk accelerating sharply at higher stress scores. Occupational stress was significantly associated with adverse mental and physical health outcomes among metal mining workers. Insomnia was identified as a potential mediating pathway, while the association with depressive symptoms was non-linear, characterized by a sharply higher risk at high stress scores. These findings underscore the need for targeted workplace interventions that address both psychosocial stressors and sleep health to improve worker well-being.</p>