A method and system for detecting brain activity may be disclosed, the method including performing multi-channel synchronous collections of brain electrical signals and cerebral cortex blood oxygen signals simultaneously and ensuring synchronicity of the collected signals among channels by collecting the signals at multiple locations simultaneously. A system may include a functional near-infrared light source emission module, which may employ the frequency division multiplexing technique. A multi-functional joint collection helmet may access the light source signal emitted from the emission module, then may be processed by a near-infrared detection module. Further, the near-infrared detection module may detect optical signals of the scalp, while a brain electricity detection module detects electrical signals of the scalp. Finally, a central control unit may synchronize data collected from the detected signals and may control a variety of functional modules and upload the data to a host computer.