Abstract: The nitinol wires in a nickel titanium alloy medical device product fractured during production. The fracture reasons of the nitinol wires were analyzed by chemical composition analysis, mechanical property test, cleanliness test, macro analysis, micro hardness test and micro analysis of fracture surface and so on. The results show that when the wires passed through the bending area of the fixed steel sleeve during the braiding process of the nitinol wires, the work hardening stress was not completely eliminated, which resulted in overload plastic fracture of the nitinol wires under large bending stress.