Abstract: Ultrasonic Time of Flight Diffraction method (U-TOFD) is adopted in testing the defects of austenitic stainless steel weld,and the influences caused by the weld structure are analyzed.Besides,the testing signal is decomposed by wavelet packed method (WPT) and the decomposed signal that fits for gray imaging is obtained.The results indicate that there are amount of noise stripes and shape torsion in the gray imagery because of the ultrasonic scattering caused by the column grain in weld,the noise level can be restrained without destroying the time resolution through choosing suitable decomposed signal.Eventually,gray imaging based on the decomposed signal is beneficial for improving the quality of testing signal and avoiding the torsion of the defect′s imagery.