Dementia is a syndrome characterized by progressive global cognitive impairment that impairs occupational, family, or social functioning. It detrimentally affects personal health and quality of life, imposing significant medical economy, social and psychological burden on the countries and the patients' family. The internationally renowned dementia cohort includes the DIAN that focused on genetics studies, the ADNI cohort featuring imaging and the FINGERS cohort focused on risk factor intervention, etc. Establishing standardized and shared longitudinal follow-up dementia cohorts and clinical database is an essential challenge for constructing dementia cohort in China. Moreover, there is a lack of large-scale prospective longitudinal follow-up cohorts within the Chinese population that cover subjective cognitive decline (SCD) to explore biomarkers with diagnostic and early warning value for different kinds of dementia and pre-dementia stages. The study will rely on the dementia cohort based on Chinese population to explore the biological phenotype characteristics of the pre-dementia stage and different dementia subtypes, and observe the dynamic change rules of the dementia cohort vertically, so as to foster early intervention and improve prognosis for individuals with dementia.