The invention discloses an online cognitive assessment system and an assessment method, and belongs to the field of assessment systems. The online cognitive assessment system comprises a terminal platform, wherein the terminal platform comprises a processor module, a power supply module, a man-machine interaction module, a communication module, a recording module, an assessment module, a storage module, a calculation module and an output module; the power supply module, the man-machine interaction module, the communication module, the recording module, the assessment module, the storage module, the calculation module and the output module are connected with the processor module respectively. Online cognitive diagnosis is carried out through reading and processing information of each module. By adopting the online cognitive assessment system and the assessment method, rapid and accurate assessment and good accuracy can be realized, and information is updated in real time.