Abstract: The paper introduced the type and mechanism of the defects of Friction stir welding(FSW), and concentrated on the development and research results of penetration testing, radiography testing, ultrasonic testing, eddy current testing for the defects of FSW. Through comparison between advantages and disadvantages of the dectection methods, it concluded that the combination of ultrasonic phased-array and eddy current array for the inspection of FSW might be able to find the defects to the greatest extent.