According to one-to-one relationship of the Binary-Phase-Shift-Keying (BPSK) fuse signals pulse-phase difference and the m-sequence, the m-sequence can be obtained by solving the phase-difference equations. First, the pulse phase is measured by FFT. Then, first-order phase difference method and second-order phase difference method separately are applied to identify the m-sequence. The computer simulation proves the method to be completely correct. Finally, the reliability of the method is analyzed to find that, even if any Pseudo Noise (PN) code is mistakenly identified because of large measuring error of the corresponding pulse phase, it has no influence on identification of the later codes. This indicates that the method has high reliability.