In view of the problems existing in the detection of complex defects in gun barrel, proposes a detection method using ultrasonic guided wave to detect single and non-single crack defects in gun barrel. Under the condition of changing the wear amount of each radial wear, the propagation characteristics of guided wave are analyzed; combined with Comsol finite element simulation software, the multivariate relationship between the radial wear size at different axial positions and the echo coefficient of guided wave is obtained, and the quantitative method of ultrasonic guided wave detection is designed. The detection can provide a theoretical basis for the comprehensive detection of gun barrel internal defects.