Evoked EEG signal can be obtained by flash stimulation in the extraction of flash visual evoked potential(FVEP).Experiments show that the width,frequency and flash times of flash pulses will play key role for extracting FVEP.Aims at the feature of VEP extraction and its correlation factors,the flash stimulation method with pulse width modulation(PWM) technology has been discussed,and the realization methods based on hardware and software are studied,then the output of precise PWM with special integrated circuit is realized.So the parameters of flash stimulation can be adjusted based on the material conditions of FVEP extraction,then VEP can be extracted effectively.Experiments show that it is of better effectiveness for FVEP extraction by using the method based on the output of precise PWM to control the flashing stimulation.