Abstract: The nickel titanium wires in a nickel titanium alloy implantable medical device product fractured during production. The fracture reasons were analyzed by chemical composition analysis, mechanical property test, cleanliness test, macro and micro fracture analysis, energy spectrum analysis and so on. The results show that the machining stress of the nickel titanium wires had not been eliminated well, and the corrosive medium introduced by the braiding rod and the heat shrinkable tube. These two factors together caused the stress corrosion fracture of the nickel titanium wires.