Alzheimer's disease (AD) is the most common type of dementia， and there is currently no specific medication that can cure or effectively reverse its progression. Dietary intervention， as a safe and widely applicable strategy， has attracted increasing attention. Numerous studies have demonstrated that dietary fiber， particularly soluble dietary fiber (SDF)， can alleviate neuroinflammation associated with AD pathology. The gut-brain axis， a critical communication pathway connecting the gastrointestinal tract and the central nervous system， with its core component-the gut microbiota-is considered a key mechanism through which diet modulates brain health. This review summarized how dietary fiber， especially SDF， modulates AD-related physiological processes by reshaping the gut microbiota. The main mechanisms included the regulation of key metabolites， immune pathways， endocrine pathways， and vagus nerve signaling. Although current research still had certain limitations， existing evidence strongly suggested that diets rich in dietary fiber hold significant potential for maintaining cognitive health. These findings also provide important theoretical support for the food industry in developing functional foods aimed at promoting cognitive well-being. In the future， research on dietary fiber and the gut-brain axis was expected to drive innovations in food ingredient utilization， formulation optimization， and the synergistic application of prebiotics. This will offer new opportunities for food research and development and market expansion in the fields of healthy aging and brain health.