The invention discloses a conscious state detection system using an invisible watching BCI (brain computer interface). The system comprises a visual and acoustic stimulation module, an EEG (electroencephalogram) acquisition module and an EEG processing module, wherein the visual and acoustic stimulation module randomly plays visual and acoustic digits with consistent and inconsistent semantics tosubjects; the EEG acquisition module records EEG of the subjects when the subjects perform specified tasks in real time; the EEG processing module outputs online detection results in real time. A visible watching visual and acoustic stimulation form is designed, and conscious state of the subjects is detected by the BCI technology. The accuracy is analyzed online and fed back to the subjects in real time, and the conscious state of the subjects is accurately detected. The conscious state of the subjects is detected by visual and acoustic stimulation with consistent and inconsistent semantics,and the detection accuracy of consciousness of the subjects is improved.