Abstract: In order to understand the effect and characteristic of phased array Phase Coherence Imaging(PCI) inspection technique, the basic theory of ultrasonic phased array TFM (total focus method) and PCI technique was introduced, the difference of TFM and PCI was analyzed detailly. According to the test results of point tip defects, planar defects, volumetric defects with PCI technique, the effect and characteristic of PCI technique were described, to promote the correct application of PCI technique in the field of industrial nondestructive testing.