Abstract: Global aging exacerbates the public health challenges posed by cognitive decline. This systematic review examines the independent and interactive effects of fine particulate matter (PM_2.5) and physical activity (PA) on cognitive function. Research demonstrates that long-term PM_2.5 exposure impairs cognitive function across all age groups through mechanisms such as neuroinflammation and oxidative stress, with older populations exhibiting particular vulnerability. Although PA exerts neuroprotective effects, its cognitive benefits exhibit a pronounced dependence on PM_2.5 concentrations. In low-PM_2.5 environments, PA may partially counteract PM_2.5-induced cognitive damage. Conversely, as PM_2.5 concentrations increase, the health benefits of exercise may gradually diminish and even reverse due to increased pollutant inhalation at high exposure levels. Current discrepancies in research findings arise from variations in PM_2.5 exposure assessment methodologies and population heterogeneity. Future research should prioritize large-scale longitudinal studies across diverse geographic and demographic cohorts. Chemical composition of PM_2.5 should be integrated with real-time air quality data to delineate context-specific PA thresholds aligned with PM_2.5 gradients, thereby providing a basis for targeted public health intervention strategies.