Under the condition of no substantial change in the crystal size of the optical interference device, in order to improve the static spectrum resolution of the spectrum analysis equipment, the optical interference system of electro-optic modulation was designed. Wollaston prism group was used on the basis of analysis of the methods for increasing scanning range of the optical path of the static interference system. In the meantime, crystal refractive index was modulated by electro-optic modulation technique, and the range of the optical path difference was derived. Finally, the synthesized optical path difference function and spectrum resolution of the system was given in a modulation cycle. Experiments used three Wollaston prisms with same size and structural angle to constitute Wollaston prism group, and the signal was modulated by type SGT-3 acousto-optic modulator devices. Experimental results show that the interference fringes image after eliminating redundant processing can be effectively fused. Modulated interference image has a little distortion, but meets the requirements to reduce the spectrum distribution function after linearity correction. The spectrum resolution increased nearly by an order of magnitude compared to the static interference with the same crystal size.