Abstract: Nyquist folding receiver (NYFR) can achieve wideband radar signal reception with a small number of devices, and measuring the waveform parameters of the received signal requires a correct estimation of the Nyquist zone (NZ) where the signal is located. Aiming at the current widely used linear frequency modulated (LFM) signal, the NZ estimation method based on time-frequency boundary fitting is optimized on the basis of analyzing the time-frequency graph of the LFM signal sampled by NYFR. The influence of the modulation coefficient and modulation frequency of the local oscillator signal in NYFR structure on the performance of the proposed method is discussed, and the NYFR parameter selection strategy is given. The simulation results show that the optimized time-frequency boundary fitting method can achieve 100% correct detection probability when the signal-to-noise ratio is better than -9 dB.