Abstract: Ultrasonic attenuation, scattering and beam distortion caused by the organization structure lead to great difficulties in ultrasonic testing of austenitic stainless steel weld. The anisotropy characteristics of ultrasonic attenuation and scattering are analyzed, and the secondary wave inspection based on ultrasonic TOFD (time of flight diffraction) method is proposed. Influences of beam incidence direction and grain direction on signal to noise ratio (SNR) of testing signal are revealed through changing the diffraction angle of testing wave in target area with the method of adjusting the probe′s distance. The research indicates that the ultrasonic propagated in the stainless steel weld reflects obvious anisotropy characters, and that higher signal to noise ratio can be acquired when the angle between the columnar grain and ultrasonic beam is small. Thus, the secondary wave method based on ultrasonic TOFD becomes very necessary when the probes cannot put on the side of the weld root, and the diffraction wave of defects in stainless steel sheet can be abstracted by the method.