The background and development of functional brain imaging are briefly reviewed. The optical imaging technologies of brain function are then introduced and classified. Several methods including voltage sensitive dyes imaging, optical imaging based on intrinsic signals, optical coherence tomography imaging, event-related optical signals imaging are summerized and compared, and the key factors of how to choose an optical imaging system recording fast brain activity are summed up. Based on the analysis and comparison, we suggest how to improve functional brain imaging technologies and point out possible directions for further research.