Abstract: In order to study effect of pressure and buffer gas on photoacoustic signal and resonance frequency, a trace gas detection system was designed based on photoacoustic spectroscopy. Taking NH₃ standard gas as an example, filling buffer gas into the photoacoustic cell to change the pressure in the photoacoustic cell, with the pressure as a single variable, the change of photoacoustic signal and resonance frequency was obtained in pressure range from 0.03MPa ~0.1MPa. And then, different kinds of buffer gases were filled into the photoacoustic cell respectively. The change of photoacoustic signal and resonance frequency in pressure range from 0.03MPa ~ 0.1MPa were obtained under different buffer gas conditions. The results show that, with the increase of pressure, the amplitude of photoacoustic signal increases. The heavier the buffer gas, the greater the increase of photoacoustic signal. The increase of pressure makes the resonance frequency shift. The shift of resonance frequency is inversely proportional to molar mass of the mixed gas molecules in the photoacoustic cell. The change of pressure and background gas makes the environment more complex and affects the detection results. This study provides a reference for solving this problem.