Resonant frequency of a photoacoustic cell is one of its key parameters. In order to measure resonant frequency of a resonant photoacoustic cell quickly and accurately, a resonant frequency measurement method based on resonant acoustic spectroscopy was used to built a photoacoustic spectroscopy detection system and a resonant acoustic spectroscopy measurement system. The factors affecting the accuracy of measurement results were analyzed. Resonant frequency of the resonant photoacoustic cell was measured by the resonant acoustic spectroscopy method and photoacoustic signal intensity method respectively in the case of different gas concentrations. The experimental results indicate that the resonance frequency measured by the resonant acoustic spectroscopy method is independent of excitation voltage of the sound signal, distance and angle of sound source. Under the conditions of 5 different concentrations of acetylene(C2H2) gas, the maximum deviation of the resonant frequency between the resonance acoustic spectroscopy and photoacoustic signal intensity method is 1.1Hz. It is considered that the measured results of both the methods are consistent. The resonant acoustic spectroscopy method is simple, fast, reliable and accurate. It can be used to determine the resonant frequency of a photoacoustic cell.