Abstract: By adjusting the number of elements, starting elements, and ending elements of the phased array ultrasonic testing instrument, virtual probes with different number of elements were formed. Two sets of experiments were conducted using RB-1 type ultrasonic testing standard test blocks under the condition of bottom echo of H=25 mm. Firstly, the gain values of each individual element of the probe were measured when the bottom echo reached 80% of the full screen height, and the fluctuation of excitation sound pressure of a single element was analyzed; Then the parameter settings were adjusted, the gain value was measured and recorded when the bottom echo of virtual probes with different array elements reaches 80% of the full screen height, the gain mean and variance mean of all virtual probes with the same array elements were calculated, and the change trend of the gain mean and variance mean of virtual probes with their array elements was obtained. Based on experimental data, the stability of probe array element sound pressure and the impact of virtual probe sound pressure on actual detection were analyzed, providing some reference for the practical application of phased array ultrasonic testing.