Abstract: Elastic module,microstructure of materials and corresponding mechanical properties can be characterized by ultrasonic methods,especially,the microstructure,a crucial factor of mechanical properties,correlating with ultrasonic attenuation obviously.In the present research,a focusing angle beam immersion system was adopted to receive the transmission wave which represents to penetrated attenuation caused by the different microstructure of friction stir welding(FSW)joints,and the feature of FSW joints had been extracted from C-scan images for non-destructive evaluation of the tensile properties of welds.A desirable correlation between the calculating and testing results of ultimate tensile strength was presented,which indicates the feasibility of predicting mechanical properties of FSW joints by ultrasonic methods.