The braincomputer interface system based on eventrelated potentials is difficult to detect the idle state of the brain, which limits the freedom of the subjects to output instructions at any time. Oddball paradigm can induce the N200 potential, P300 potential and transient visual evoked potential simultaneously. the working state and idle state of the brain are distinguished according to the frequency domain characteristics of transient visual evoked potential. In the working state, the timedomain features of N200 and P300 potential are used to identify the control intention of the subject. Through the experiment of sending instructions and watching video feedback on seven healthy subjects, the switch between the working state and the idle state of the brain is realized. The accuracy of the method to identify the state or intention of the brain is 98.21%, which is 50.89% higher than that of the method to identify the idle state based on the eventrelated potential.