Abstract: Duplex stainless steel is widely used on process piping due to its good characteristics in strength, plasticity and toughness. But nondestructive testing methods such as RT and manual UT while used for the weld seam of the steel shall meet some difficulties and challenges, so this article introduces a method of using phased array ultrasonic testing based on TRL probe. Through transmitting and receiving the sound wave separately, the probe has high signal-to-noise ratio, and the reliability of the method has been proven by demonstration block and site inspection.