Abstract: Thin-walled titanium tube is widely used as heat-exchange tube in nuclear power plant, and nowadays the inner ET testing is wildly used in titanium tube in-service inspection. In this paper we tested the sample tube with dents by ET tester, and made a comparison between the results, and then we found the linear relationship between signal amplitude and the dent area. Based on that, we provide a method to evaluate the dent degree of tubes quantitatively.