Abstract: In order to explore the influence of the number of excited wafers, the activation aperture and the depth of focus on the detection sensitivity in the phased array ultrasonic testing process, through experiments, the detection sensitivity for a series of different depths of transverse through holes by 55° shear waves was determind under three sets of activation apertures and different focus depths. The effects of different focus depths on sensitivity under fixed aperture conditions and the relationship between different activation apertures and focus depths and sensitivity under fixed aperture depths are studied. Experimental results show that focusing will increase the sensitivity at the focal point, and in most cases the larger the effective wafer area, the higher the sensitivity, but after passing the focal point, the sensitivity will decrease faster than in the unfocused state. Therefore, in actual detection, for different detection areas, a suitable detection process should be selected according to the sound field energy distribution of different probes to obtain a more optimized detection effect.