Abstract: At present time, steady-state visual evoked potentials (SSVEP) are highly applied in brain-computer interface and clinical diagnosis and therap. It is equally important to understand the influencial actors and the laws on the SSVEP. There are many differences between the SSVEP evoked by visual flicker with different duty-cycle in different experiments, so it is hard to summarize the common rules of the SSVEP changing with the change of the duty-cycle of the visual flicker. The membrane current of the visual neurons inducing action potential is taken as a magnetic dipoles to build the computational models for the electric fields in the head and the SSVEP on the scale of the human in this paper. Then the basic rules of the duty-cycle of the visual flicker influencing on the SSVEP were researched according to the computational model and the experiments were completed accordingly. The results show that under the conditions of the same frequency and intensity of the visual flicker, the variation curves of the harmonic amplitude and the average power of the SSVEP change along with the change of different duty-cycle of the visual flicker show several "window" patterns. The results of the experiments agree with that of the theoretical studies.