Abstract: When circumferential ultrasonic testing is performed on cylindrical item with thick wall, the testing sensitivity of internal surface radial defects is affected by various factors. The authors systematically analyze the characteristic of SW technique, double wave modes technique, small angle LW tangent internal surface technique, deformation SV corner-echo technique and deformation SW tangent internal surface technique, based on the investigation of technical problems of circumferential ultrasonic testing for internal surface radial defects in cylindrical item with thick wall. The formula of ultrasonic echo of internal surface radial defects detected using above techniques is presented based on theoretical analysis. The ultrasonic testing sensitivity experiments are performed on test samples with artificial internal surface radial defects, and the experimental results are analyzed and discussed.