To address the low signal-to-noise ratio in defect detection caused by high noise levels and complex modes of ultrasonic signals of thick-walled austenitic stainless steel welds，a total focusing method based on a one-transmitter，one-receiver longitudinal wave（TRL）dual-matrix array with variable mode decomposition（VMD）noise reduction was proposed. Transverse hole defects with a depth of 10-70 mm and a diameter of 3.2 mm were machined on the austenitic stainless steel weld test block with a thickness of 76 mm，and a TRL probe with a center frequency of 2.25 MHz was selected to collect full matrix capture（FMC）data. The grey wolf optimizer was used to optimize the penalty factor coefficient and decomposition level of the VMD of the FMC signal，and the full data matrix was reconstructed according to the spectral energy distribution and cross-correlation coefficient of the modal components. The superposition rule for the acoustic beam propagation delay in three-dimensional space was established，and the FMC noise reduction signal was imaged using the total focusing method. The results showed that the defect signal-to-noise ratio of the VMD denoising imaging increased by 4.69-6.85 dB compared with the imaging results of the original FMC data，thereby effectively improving the weld detection effect.