A new method is proposed to improve the low-pass characteristics of the zero-phase Hilbert low-pass filter affected by periodic repetition of the frequency spectrum caused by time discretization changes in numerical calculations. The frequency response characteristic of the time domain analytical expression of the filter was demonstrated to prove that, in the numerical calculation, Hilbert low-pass filter frequency response characteristic retained phase inversion components on both sides of π. Then, the numerical calculation method was improved using a two-stage filter according to the pattern of frequency response characteristic graph, and the zero-phase low pass could theoretically be achieved. The amplitude modulation and amplitude modulation-frequency modulation simulation verified the characteristics of the proposed filter. Finally, the improved filter was applied on dynamic stain data of a field test to eliminate the temperature influence of low frequencies. The results showed that it was suitable for nonstationary signal preprocessing.