Abstract: The reliability of ultrasonic phased array for butt weld is analyzed to provide references for the ultrasonic phased array inspection standard by comparison with conventional ultrasonic inspection. Simulations and experiments showed that, the defect detecting rate of phased ultrasonic testing method is higher than general ultrasonic testing method in totally. For the seriously hazardous defects and also plane defects with highly ultrasonic beam direction, phased ultrasonic testing can get a higher detective rate than general ultrasonic testing. For the voluminal defects such as slag inclusion, incomplete fusion and so on, there is a high detecting rate for both phased ultrasonic and general ultrasonic testing. But for the small voluminal defect such as porosity, phased ultrasonic testing can get a higher detecting rate than general ultrasonic testing method. For the thick weld seam, using phased ultrasonic testing method can scan the deeper depth of the seam than general ultrasonic testing. For the defect length measurement, phased ultrasonic testing get a longer defect size than general ultrasonic testing method, therefore there is no obvious advantage on the size measuring accuracy for phase ultrasonic testing than general ultrasonic testing method.