Abstract: A new ultrasonic method, which is based on reflection of spot-focused beam with different incident angles, for evaluation of defects in aluminum alloy friction stir welding(FSW) has been investigated. The relationship of incident angles, possible defect directions and thickness of defects in FSW with reflective coefficient has been used to analyze and estimate scanning incident angle range of probe beam. The optimum ultrasonic reflection direction can be obtained during the scanning of incident angles. It is helpful to improve detectability of defects in FSW. The experimental results presented have shown that ultrasonic evaluation based on multiple-incident angles has potential usage in nondestructive inspection of FSW.