Abstract: The advantages of phased delay ultrasonic nondestructive testing technology were analyzed by elaborating the principle of phased focus and phased deflection. The three-dimensional output image of top beam detection was given at 9102 full-mechanized caving face in Maying Coal Mine. The research and application results indicated that phased focus and phased deflection, or their permutation could complete the accurate and reliable detection for mechanized caving equipments with relatively complex geometric figures, and the three-dimensional output image could effectively judge the defect development tendency and device late failure form, which could raise the mechanized caving equipment life and ensured economic and efficient mining.