Abstract: The software-based global navigation satellite systems(GNSS) signal simulator would be an enormous asset for the efficient development of GNSS receivers, due to its flexible structure, the possibility for easy updates and changes and low cost. A hybrid GPS/Galileo intermediate frequency(IF) software-based signal simulator was proposed. The architecture and implementation description for it are included. This hybrid IF signal simulator consists of the following main parts, i.e. GPS/Galileo satellite constellation simulation, receiver trajectory generation, propagation and disturbance channel (including the ionosphere model, the troposphere model, the multi-path model and etc.), and GPS/Galileo IF signals generation. Meanwhile, the hybrid GPS/Galileo IF signal generator was presented in detail, which provides the following signals: GPS L1 C/A, Galileo E1 CBOC(composite binary offset carrier), Galileo E5a and E5b signals. Finally, the power spectral density (PSD) curves for the IF signals obtained with the hybrid signal simulator were given. From the PSD point of view, the implementation of the hybrid signal simulator was validated.