Objective To understand adults′ dementia-preventing health belief and its influencing factors, so as to provide reference for developing primary prevention strategies for dementia. Methods A total of 666 adults from the central and western regions of China were investigated through web using the general information questionnaire, dementia prevention knowledge questionnaire and Chinese version of the Motivation to Change Lifestyle and Health Behaviours for Dementia Risk Reduction scale (MCLHB-DRR). Results The total score of MCLHB-DRR in the adults was 93.31±12.84, and among the 7 subscales, the subscale of general health motivation scored the highest, and perceived susceptibility and severity scored the lowest. Regression analysis result showed that, gender, age, family history of dementia and dementia prevention knowledge level were the main factors influencing adults′ dementia-preventing health belief （P＜0.05,P＜0.01）. Conclusion The dementia-preventing health belief among adults in central and western regions of China is at a medium level, and it is affected by multiple factors. It is necessary to pay attention to the male, middle-aged and young people and the adults with a family history of dementia, and strengthen health education of dementia prevention knowledge through multiple channels, so as to enhance people′s health belief in dementia prevention and improve their dementia prevention behavior.