Abstract: Grade I low pressure turbine blade in engine fractured at the R bottom of tenon. In order to find out the failure mode and cause, macro and micro examination, span bar distancetesting, stress calculation for tenon and simulation fatigue test were carried out. The results show that the fracture of the blade is multiple-source linear fatigue fracture. In the aluminizing process, due to the improper protection of the tenon, the tenon was contaminated by the aluminized layer, and the span bar distance of the tenon is extremely poor, which reduces the fatigue resistance of the blade, and eventually leads to fatigue fracture of the blade. For this batch of engine blades, if the thickness of aluminized layer is within 0.03 mm and the span bar distance is qualified, then the blade can be used. By strictly monitoring the blade tenon and increasing the span distance measurement, and adopting strict protective measures, such failure can be effectively avoided.