BPSK signal has been widely applied in new radar systems. The obtainment of Doppler frequency rate-of-change from BPSK coherent pulse signal is a key technology in the passive locating and tracking system of single observation. The influence of phase modulation is dismissed by square method and DFT (Discrete Fourier Transform) is used to realize the coherent integration between the pulses. This algorithm has small computation and high estimation precision of Doppler frequency rata-of-change. The computer simulation results show that the precision of parameter estimation meets the needs for passive locating and tracking system of single observer.