Abstract: The fast increase of aging population in global leads to the prevalence of aging-associated neurodegenerative diseases, which places a substantial socioeconomic burden on the whole society. However, aging is a multifactorial process determined by genetic and environmental factors. The development of validated neuroimaging-based biomarker is essential for the risk assessments and predictions of age-related neurodegenerative diseases. The brain age gap estimation is the most widely used measure for assessing brain health status based on magnetic resonance images (MRI). This review first introduced the research progress of brain aging based on MRI and brain age estimation model based on neuroimaging, then summarized and discussed the findings on BrainAGE as a biomarker from the aspects of genetics, brain development, neurodegenerative diseases, psychiatric diseases, chronic diseases and cognitive reserve. Finally, the existing problems and future research direction were put forward.