Abstract: High-frequency ultrasound is widely used in wafer fabrication and electronic packaging, and can effectively detect defects such as holes and delamination in materials. The acoustic impedance of discontinuous defects such as internal cavities and delamination is often lower than that of the material itself, and the phase of the internal defect echo should be reversed compared with the surface echo of the material during water detection. The acoustic effects of phase reversal were analyzed. The time-domain and frequency-domain characteristics corresponding to ultrasonic signal phase reversal were studied. A phase inversion recognition method based on time-domain signal envelope was proposed. The accuracy and efficiency of phase reversal calculation methods in time-domain and frequency-domain were compared. The results of chip high-frequency ultrasonic imaging showed that the time-domain feature recognition method had higher efficiency and accuracy, and the gate threshold could effectively suppress noise, while the frequency domain recognition method had lower efficiency and was more sensitive to noise.