Abstract: The conventional ultrasonic inspection method for the low-pressure cylinder can only check the surface defects, the defect in the experience feedback mentioned in the blade root is difficult to detect. In this paper, using the ultrasonic phased array inspection technology, the development of low pressure rotor grades at the end of the final blade root phased array inspection technology system, can defect detection of blade root. The technology system mainly includes the phased array specimen development, special test probe design and test technology development, etc.