The invention discloses an image de-noising method for coarse austenite stainless steel welding line ultrasonic detection, and belongs to the field of ultrasonic nondestructive detection. The method comprises the following steps: at first, detecting a welding line by an ultrasonic detection system, which comprises a flaw detector, a probe, and a scanning apparatus, to obtain an ultrasonic image, outputting A scanning signal data that forms the ultrasonic image; then reconstructing the ultrasonic image through a signal time shifting and amplitude addition treatment; finally extracting the phase information of A scanning signal through Hilbert transform, establishing weight factors representing the phase position distribution of each point of the ultrasonic image on the basis of standard deviation of phase position, and amplifying the contribution of signal phase position distribution on flaw echo amplitude in the ultrasonic image to inhibit the noise amplitude of structure with randomly distributed phase positions. The provided method can be used to detect the ultrasonic defects of a coarse grain material and has a good application and promotion value.