Abstract: During the construction of offshore oil platform, a great quantity of pipe longitudinal weld joint welded by one side and TKY tubular joints will be used. This kind of joint weld often requires 100% ultrasonic inspection to determine whether there are defects in the weld. Because of the change of root edge angle and probe scanning surface curvature, the ultrasonic echo forming in the root of weld is very complex. The test blocks of root reflector with different inclination angles are made, and the root ultrasonic echo caused by the change of innclination angle is analyzed.