With the development of mechanical equipment towards large-scale and complexity, the size and operational reliability of its key core components is gradually improved. Aiming at the problem of large radial structure size and high mechanical performance of MP1000 miner forging spindle, but low efficiency and reliability of ultrasonic nondestructive testing, which makes it difficult to detect uneven material in forging process, the finite element numerical simulation of ultrasonic flaw detection process of forging spindle is carried out by using software. By analyzing the locations of ultrasonic probes on different buses on the surface of the spindle, the edge areas of the steps and the processing of the ultrasonic probe, the problem is analyzed. The instantaneous distribution of the sound field in the hole position is summarized. The design method of UT testing special tool for large forging spindle is summarized, and the corresponding testing unique tool is designed. This tool can cooperate with UT equipment to effectively detect the uneven defects in the material of shaft parts and effectively improve the detection efficiency of ultrasonic nondestructive testing in the application of heavy forging spindle parts.