By continuously injecting four groups of heterogeneous frequency dual pulses into the sensing fiber with weak fiber Bragg gratings (WFBGs), a quasi-distributed acoustic sensing method based on frequency-division multiplexing is proposed. Each group of pulses generates interference signals with different carrier frequencies after being reflected by the WFBGs. Through the discrete Fourier transform phase demodulation method, each carrier frequency interference signal is demodulated and then the phase is spliced. The feasibility of this method is theoretically analyzed, and a detection with a bandwidth of 2 kHz is realized on a 70 km sensing fiber with a spatial resolution of 10 m.