Abstract: The integrity of T type load-carrying welding parts of aluminum alloy is one of the key factors to ensure the safety of high-speed train, eddy current testing is suitable for the testing of the aluminum alloy components with multiply advantages such as no coupling medium. However, the signal to noise of defect detection signal interfered with the morphology of welding fish scale pattern is low. The finite element method adopted to establish the defect detection model of aluminum test plate with the painting layer. The simulation result indicates that the inner wall of the excitation coil is 8 mm × 4 mm (Length × width), the thickness is 0.1 mm, the height is 1.5 mm, the coil placement angle is 45°, and the detection sensitivity is the best when the excitation frequency is 400 kHz. The simulation and test results verify that the welding eddy current probe can detect the welding crack defects of T type load-carrying components of aluminum alloy with the painting layer effectively.