In order to explore the acoustic characteristics of shale affected by carbonic acid (H2CO3), taking the marine shale in Xiuwu basin as the study object, the ultrasonic transmission test was used to study the characteristics of time domain signal, wave velocity, frequency domain signal, and attenuation coefficient of H2CO3-treated shale. The results show that, compared with dry shale, the propagation time of P- and S-wave of aqueous shale is prolonged, and the amplitudes of P- and S-wave present obvious decline. Under the same conditions, the amplitude of first P-wave is stronger than that of the first S-wave, namely, the transmissibility of P-wave in shale is stronger than that of S-wave; the maximum amplitude in frequency domain decreases, the dominant frequency shifts to low frequency, and the dominant frequency of some samples is distorted; the velocity of P- and S-wave decreased, and the attenuation coefficients of P-wave and S-wave increased. It is concluded that shale porosity increased or fracture produced induced by acidification.