The frequency drift phenomenon exists in both the acousto-optic modulator and laser of the phase sensitive photosensitive time-domain reflection (Φ-OTDR) system, leading to phase shift and amplitude fluctuation in the demodulated signal, which affects the accuracy of vibration signal detection. This paper proposes a Φ-OTDR system structure based on dual acousto-optic modulators, adopting heterodyne detection to construct the local oscillator and sensing signals with the same frequency drift, thereby overcoming the influence of frequency drift in the backward Rayleigh scattering optical signal of the sensing fiber. The optical signal output by the laser is divided into upper and lower branches. The signals in these two branches are then passed through two acousto-optic modulators and two optical splitters, respectively, generating four frequency-shifted optical pulses in total. One of the optical pulses in the lower branch enters the sensing fiber, and its backward Rayleigh scattering signal interferes with one of the optical pulses in the upper branch, generating a sensing beat signal. The other two pulses generate the local oscillator beat frequency signal, which after coherence have the same frequency drift effect. The frequency drift issue is resolved through quadrature phase demodulation. This study establishes an orthogonal demodulation model, to suppress frequency drift. By theoretically deducing and analyzing the mechanism of this model, frequency drift was suppressed. The feasibility of the dual acousto-optic modulator system in suppressing the influence of frequency drift was further verified through simulations.