Abstract: Aiming at the simulation problem of ultrasonic phased array transient sound field in multi-layer anisotropic austenitic stainless steel welds,it is proposed to apply the Gaussian sound beam equivalent point source model to calculate the broadband discretized multiple single-frequency steady-state sound fields which will be extended to transient sound field by Fourier transform,and the main influencing parameters of the sound field conversion process are analyzed.This method can quickly calculate the transient energy distribution of the ultrasonic phased array focused sound field inside the welds and the time-domain waveform at any point.On this basis,in order to solve the problem of ultrasonic phased array imaging detection of internal defects in multi-layer austenitic stainless steel welds,it is proposed to use the abovementioned time-domain Gaussian beam method to calculate the time inversion of the multi-channel defect scattering signal and determine the defect location according to the focus of time-domain sound field.Finally,the effect of this method to detect the internal defects of the actual austenitic stainless steel welds test block is verified by experiments.The results show that the proposed method can determine the positions of the defects.The calculation speed is fast and the calculation amount is small.It is a suitable real-time imaging method for the internal defects of the multilayer medium.