Abstract: A titanium alloy flexible shaft for drilling had a bright band at the reducer near the plug end after a period of drilling and start-up. The cause of the bright band was analyzed by force analysis, macroscopic and microscopic morphology observation, chemical composition analysis, mechanical property test, and finite element simulation. The method of prolonging the life of titanium alloy flexible shafts was put forward. The results show that fretting wear occurred at the reducer of the flexible shaft, and the fretting wear was mainly caused by the shear stress and the relative displacement between body part of flexible shaft and plug parts. The fretting wear resulted in the initiation of cracks at the reducer of the flexible shaft. Under the alternating load and torque, the cracks propagated, resulting in the fretting fatigue. The cracks originated uniformly from the periphery and propagated with transgranular forrn. The surface hardness and wear resistance of the titanium alloy increased after the coating layer was prepared by supersonic flame spraying technique, which could restrain the peripheral origin cracks caused by fretting wear, thus prolonging the life of the flexible shaft.