Abstract: After a TC6 titanium alloy mount running on aero-engine, and it was disassembled for fluorescent inspection, a linear fluorescent indication with a length of about 4 mm was found at the arc of the mount. The causes of fluorescent indication defect were analyzed by means of macro observation, micro analysis, metallographic examination, hardness test and energy spectrum analysis. The results show that the fluorescent indication defect on the mount was a fatigue crack. The integrity of the circular arc surface of the mount was destroyed during grinding with artificial wheel grinding, and the fatigue crack source was formed. During the test run, the crack propagated and connected with the forging folding crack which was not completely removed, and finally the defect formed.