Global navigation satellite system(GNSS) signal simulator can simulate satellite signals received by target receivers in high fidelity according to the signal structure, dynamics of the receiver and environmental parameters defined by users, which provides an effective way for both GNSS system-level simulation and receiver test. The research of GNSS IF signal generator and digital signal processing techniques of the simulator compatible with multi-systems and multiple carrier frequencies was mainly focused on. Approaches on digital signal synthesis, power control and accurate simulation of signal phase were proposed. Functions of communication with PC, calculation and updating of waveform controlling parameters, baseband signal modulation and generation of analog IF signal were implemented on the IF signal modulator based on the architecture of PCIE+DSP+FPGA+DAC. Test results from the corresponding GNSS receivers validate the accuracy and quality of signals generated by simulator.