For researching the factors affecting second-harmonic generation in photorefractive crystal, based on the generation theory of the phenomenon of frequency multiplication in optical second-harmonic, the multiplication frequency phenomenon of spatial frequency in self-defocus LiNbO3 crystal is found. The generation states of second harmonic are controlled by interference method through changing the parameters of amplitude mask in optical path. The results show that the generation quantities of split strip are affected by the quantities of light source. The generation of second-harmonic is affected by periodic waveguide. When the quantities of light source and periodic waveguide are constant, the second-harmonic will appear more quickly and obviously with the increasing of optical intensity.