Abstract: It is necessary to measure the size of the zirconium alloy pipe when the pipe is tested. In this paper, a measuring method for the diameter of laser and ultrasonic thickness is introduced in the ultrasonic automatic flaw detection system for pipes. Through the application and test of a zirconium alloy pipe, the error of the outer diameter measurement is <±0.008 mm, the wall thickness measurement error is <±0.02 mm, and the inner diameter measurement error is <±0.025 mm, which is able to meet the requirement of pipe production.