A virtual-block-array phase analysis method is proposed for the fiber-optic distributed acoustic sensor. The sensing fiber is divided into a serial of discrete virtual blocks according to the pulse spatial length. The phase variation caused by acoustic events is obtained by combining the operation of the temporal differential process between traces and local spatial average in virtual blocks. The linear frequency-modulated probe pulse produces phase compensation effects at the event location. High signal-to-noise ratio (SNR) measurement is verified by simulation and experiment. The reconstructed waveform of 1.5 kHz sinusoidal signal showed a root mean square error of 0.0359 and an SNR of 47.28 dB.