The frequency stability of CO2 pumping laser is of great importance for optically pumped terahertz(THz) gas laser. Aimed at frequency stabilization technique based on photoacoustic effect, the influence of detective conditions on the detection of weak photoacoustic signal in photoacoustic cell was theoretically analyzed and numerically simulated and the detective conditions were further optimized for high-precision detection of photoacoustic signal, including the pressure of methanol gas and the microphone sensitivity. On the basis, the variation of photoacoustic signal with the frequency shift of the pump laser from the center of the absorption line was analyzed. The results show that the low pressure condition and highly sensitive microphone are the keys for achieving high-precision photoacoustic frequency stabilization. When the laser frequency of CO2 pumping laser shifts from the center of the absorption line, the cavity length can be adjusted accurately by the regulation of feedback photoacoustic signal to ensure the frequency stability of output laser, and the frequency shift could be controlled within the magnitude of megahertz.