Aiming at the lack of effective detection methods for micro-crack defects in the blades of coated single crystal superalloy turbines, the feasibility of eddy current detection method was explored and verified. A set of eddy current detection system was established to detect and identify defects at different depths of IC21 single crystal superalloy blades with thermal barrier coating, and the impedance amplitude variation was analyzed. Video microscope (DM), scanning electron microscope (SEM), metallographic microscope (OM), and energy dispersive spectrometer (EDS) were used to carry out the appearance inspection, anatomical analysis, metallographic examination, fracture analysis, and composition analysis of the defective blades to determine the nature and cause of the abnormal signals detected by eddy current. The developed eddy current probe has high sensitivity and can accurately detect prefabricated defects on complex curved surface single crystal superalloy turbine blades with thermal barrier coating. With the increase of defect depth, the amplitude of eddy current impedance signal increases. When the crack penetrates the blade matrix wall thickness, the amplitude of impedance signal reaches the maximum. The crack morphology of the IC21 single crystal superalloy high pressure turbine blade is similar to that of the original casting surface, and no obvious single crystal fracture characteristics were observed. The γ' phase of the blade matrix maintains a good cubed structure, indicating that the single crystal superalloy turbine blade has not experienced overtemperature during use. The eddy current testing platform can effectively detect about 2.3 mm×1.0 mm crack defects in turbine blades of single crystal superalloy with thermal barrier coating, and the research results effectively fill the gap in the detection method of micro-crack defects in the matrix under the thermal barrier coating. The failure analysis confirmed that the crack of the IC21 single crystal superalloy high pressure turbine blade was caused by the original recrystallization defect, and the process did not clearly require the conical convex of the cast to be repaired, which affected the detection and identification of recrystallization defect during corrosion inspection, which was the main reason for the cracking of the turbine blade. In view of this crack defect, it is suggested that proper casting and testing process optimization of the blade should be carried out to avoid missing detection of the original recrystallization defect.