Global population aging is leading to a significant increase in cognitive disorders. Mild cognitive impairment (MCI) is a critical transitional stage between normal cognitive aging and dementia, with approximately 10–15% of individuals progressing to dementia annually. The Health Belief Model (HBM) is an established framework for understanding health behavior change, but its application in the primary prevention of MCI lacks evidence from rigorous randomized controlled trials (RCTs). This study evaluated the efficacy of a comprehensive HBM-based intervention in promoting cognitive health behaviors, delaying cognitive decline, and improving quality of life among community-dwelling older adults, and explored the mediating roles of self-efficacy and perceived benefits. A 12-month, single-blind, parallel-group RCT was conducted. 240 cognitively normal adults aged ≥60 were recruited and randomly assigned to an intervention group (n = 120) or an active control group (n = 120). The intervention group received a 6-month “Health Belief Empowerment for Brain Health” program targeting core HBM constructs, while the control group received standardized routine health education. Outcomes were assessed at baseline (T0), post-intervention (T1), and 6-month follow-up (T2). Data were analyzed using Generalized Estimating Equations and bootstrap mediation analysis. The retention rate was 94.2% (n = 226). The intervention group showed statistically significant improvements across all outcomes at both T1 and T2 (all P < 0.001). Specifically, they demonstrated substantially higher health behavior scores (T2: 108.7 ± 11.2 vs 87.5 ± 13.0) and maintained stable cognitive function (MoCA T2: 26.9 ± 1.3 vs 25.8 ± 1.5). All HBM constructs, particularly self-efficacy and perceived benefits, showed significant enhancement. Mediation analysis revealed these two constructs jointly accounted for 58.7% of the total intervention effect on sustained health behavior change. This first RCT robustly demonstrates that a systematically developed HBM-based community intervention is an effective strategy for primary prevention of MCI. Its success is predominantly driven by enhancing self-efficacy and perceived benefits, supporting the integration of such theory-driven programs into public health strategies for healthy cognitive aging.