Abstract: Using wide field pulse scanning acoustic microscope (WFPSAM),ultrasonic C scanning image for typical weld defects samples have been studied. The results show that the two dimensional acoustic images of weld defects can be obtained in different deep layer by means of C scanning function of WFPSAM. The shape, position, distribution and direction of weld defects in every deep layer can be direct observed from the two dimensional acoustic images. The weld defects size(including length, width and dimension of dispersed small defect, distribution range of concentrated defects) can be obtained, according to the defect image and chosen scanning parameter. The three dimension image of sample can be obtained by piling up C scanning image in different deep layer with the image processing technique of computer or the geometric drawing method. The stereo image, three dimensional size, space distribution of weld defects can also be detected, therefore, the accurate basis for calculation of fracture mechanics in safety assessment of welded construction are provided.