Abstract: Galileo signal simulator can provide not only a good simulation environment for design and test of Galileo receivers, but also a platform for verification of new techniques and new schemes of Galileo system. In this paper a software IF signal simulator for Galileo Satellite Navigation System in E1 frequency band designed on C++ platform is proposed. Based on mathematic model of IF signal and principle diagrams of the software IF signal simulator presented in this paper, the design is further divided into 5 functional parts, which are respectively pseudo-random code producing, navigation message generating, MBOC modulation of signal, simulation of environment error and quantification. The idea and the flow of the design are detailed presented as the key point. At last the validity of the design is demonstrated by the simulation results of frequency spectrum and capturing of output signal.