A IF acquisition and processing program is designed for vector network analyzer with double ports in this paper. The monolithic A/D converter is adapting to instead of multiple or multi-channel A/D converters to acquire and process the three channel IF signals by time-sharing data acquisition technology in vector network analyzer with double ports. The time-sharing acquisition control signal, sampling clock signal and NCO reference clock signal are achieved by frequency multiplication and counting frequency division methods in FPGA according to the frequency and phase stabilization characters of reference IF signal. Then, the acquisition and processing for variable IF is realized by IF phase-locked and time-sharing acquisition control technologies. The experimental results show that with the monolithic A/D converter to acquire and process the three channel IF signals, the volume and power consumption of the PCB is reduced by 2/3, and the dynamic range is up to 100 dB. The program is suitable for variable IF processing.