Abstract: The convex phased array probe was adopted for internal testing of bimetallic turbine disk. Focusing on defective structural features of small-bore turbine disk junction surface and in accordance with the structural features of thermometal turbine disk and connection features of diffusion welding process, it firstly conducts theoretical analysis on the sound field performance of ultrasonic phased array, and then uses CIVA simulation software to design a 8-array convex phased array energy converter. Suitable phased array parameters are selected to effectively restrain the beam spread in disk and get good focusing effect in turbine disk test block. Detecting results indicate that the designed ultrasonic convex phased array probe can focus small bore diameter in long distance, with good focusing effect, and can accurately position defects. Its detection accuracy can reach 1mm flat-bottomed hole equivalent.