Abstract: The intermittent laminate of wing plate for steel construction in thermal power plant was Ⅴ grade based on A-scan pulse-echo ultrasonic inspection while the standard of JB/T 4730—2005 was conducted. So A-scan pulse-echo ultrasonic inspection could not satisfy the requirement of monitoring. In order to solve the problem, phased array ultrasonic technology was applied. The experiment indicated that phased array ultrasonic technology could monitor the intermittent laminate based on resolution, sensitivity and reflected wave amplitude. The monitoring method and crucial parameter were proposed, which provided reference for safe operation of thermal power plant.