Abstract: Thick-walled austenitic stainless steel poses challenges such as scattering attenuation, structural noise, and beam distortion to ultrasonic testing due to its strong elastic anisotropy. Traditional phased array ultrasound techniques and detection methods based on TRL (dual crystal longitudinal wave) array probes have limitations such as restricted imaging range and poor performance in non-focused areas, resulting in low detection efficiency and limited accuracy. An imaging technique combining TRL array probe scanning and synthetic aperture was proposed. By virtually extending the probe aperture, the single imaging coverage could be expanded, and by synthesizing acoustic field information from multiple small apertures, scattering and structural noise could be effectively suppressed, improving the imaging signal-to-noise ratio. This provides a more efficient and precise solution for phased array ultrasonic testing of thick-walled austenitic stainless steel welds.