Abstract: During the fault detection after the test run of an aero-engine, the linear indication of a stage turbine blade was found by fluorescent penetrate testing. In order to determine the formation reason of the linear indication, the indication area was cut and it can be determined by physical and chemical analysis that the linear indication was a hot crack, which was generated in the casting process and did not expand during the test run. Combined with this conclusion, the reason was analyzed why crack was not detected in the X-ray inspection process and fluorescent penetrate testing process in the manufacturing stage of turbine blades and the reasons for the formation of cracks. Corresponding improvement measures for casting process and nondestructive testing process were formulated.