Abstract: After machining the tenon of a TC6 titanium alloy blade, it was found that there were cracks distributed laterally along the blade body at the back side. The causes of blade cracks were analyzed using macroscopic observation, fracture analysis, metallographic examination and hardness testing. The results show that the cracks originated from the surface of the blade back side and extended toward the blade basin side. During the high-temperature forging process, oxygen absorption reaction occurred near the surface of the blade, resulting in oxygen-enriched α-case. During the tenon machining process, the blade bore a certain amount of bending load, and the surface of the area with a large thickness on the back side of the blade bore a large stress. Bending load during tenon processing and oxygen enrichment during thermal forming oxygen-enriched α-case promoted crack initiation and propagation.