Abstract: Estimating the original Nyquist zone (NZ) of a signal is the fundamental problem of using Nyquist folding receiver (NYFR). Aiming at this problem, a method to determine the NZ of poly-phase code signals intercepted by NYFR. Firstly, the Linear frequency modulated (LFM) signal and the multiphase signal are distinguished from other signals by analyzing the time-frequency distribution changes of the multiphase signal before and after NYFR sampling. Then, the NZ of the signal is determined by combining instantaneous autocorrelation and spectral peak search. The simulation results show that when the Signal is located in the same NZ, the correct detection probability (PCD) of the proposed method can reach 100% when the signal-to-noise ratio (SNR) is better than -8 dB. When the Signal is across NZ, the PCD can reach 100% when the SNR is better than -4 dB.