Abstract: Due to the manufacturing process, the thickness of the inner and outer tube walls of the double-layered tube may increase or decrease, and the axiality correspondingly changes, resulting in the change of the interval of double-layered tube. In this paper, a method of ultrasonic testing method by filling medium was used to measure the interval. The measurement results were compared with the results of three-coordinates measuring machine. It is concluded that the measurement result of ultrasonic testing method is accurate and suitable for the interval measurement of the double-layered tube.