Abstract: Brain imaging is a hot spot field in the biomedical engineering research. Current traditional brain imaging modalities, such as X-ray, magnetic resonance imaging (MRI) and other methods, are mature and have been widely applied for scientific research and clinical diagnosis and treatment comprehensively. However, most of these imaging techniques have limitations such as invasiveness, bulky equipment, and high imaging costs, and are difficult to apply to special populations, such as neonates. This paper introduces several microscopic optical molecular imaging modalities that can be used for brain imaging. Most of these methods are non-invasive, low-cost and excellent in performance, and have broad development prospects. After giving their imaging principles, system components, and key techniques, the existing research results and the current state of these imaging modalities are summarized. Finally, the future development directions of the brain imaging techniques are discussed through enumerating and comparing the merits and limitations among these imaging modalities.