Aiming at the deficiency that the forecasting wide gate has another radar signal in the traditional passive radar seeker signal processing system, phase shift and carrier frequency were researched. The trend of the phase shift was well predicted by making a phase accumulator and a logic controller in FPGA, and then the phase threshold and precise narrow gate were proposed. Since the design was based on FPGA, a lot of DSP resources were saved, the system complexity was reduced, the tracing precision was improved, and good effect was achieved in practical application.