Weld"s performance is one of the key factors that determine the application success of solid expandable profile liner technology. So far, there is no method of weld defects detecting and evaluation basis.SX-Ray digital imaging system combined with image processing software is used to detect welding defects. The technology can accurately detect the type, size and location of defects and the detection accuracy can reach 0.01mm.Three kinds of typical weld defects, gas pore, incomplete penetration and crack, were analyzed to impact on the performance of the expansion. According to crack opening displacement, the article calculated failure load of crack weld based on the method of extended finite element method and found out failure load of weld with gas pore and incomplete penetration by using nonlinear finite element method. We gained the critical size that could cause weld leakage at 30MPa pressure. Some artificial specific defects were processed on welds and welds" expansion properties were tested by hydraulic pressure. Test results verify that calculation results are reliable. The research results provide a method for the weld defects detection of solid expandable profile liner technology and provide the basis for the weld performance evaluation.