Abstract: According to the work force environment of turbine fir tree and the on-site distribution of crack, a reference block with appropriate crack was designed. Phased array inspection technique was used to detect the defects of the reference block, and the results showed that the smallest and largest size defects of the machined groove could be detected and the impeller alveolar structure signal could all be identified clearly. The design of this reference block validated the research of phased array ultrasonic testing technology in steam turbine disc.