Abstract: For the high-sensitivity inspection requirements of large-thickness parts of powder metallurgy superalloy, total focusing method using ultrasonic annular array was proposed. The feasibility of the method has been verified from the detection sensitivity, signal-to-noise ratio and near-surface resolution. Comparative experiments have been carried out with the multi-depth focusing method of conventional phased array technique and it shows that total focusing method has significant advantages in consistency of detection sensitivity and near-surface resolution. The research work provides an advanced and feasible technology for the detection of micro-defects in powder metallurgy superalloys.