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The fatigue properties and fracture mechanism of TC21 titanium alloy notched specimens in two kinds of corrosive environments (tank water, 3.5% NaCl aqueous solution) and room temperature air environment were studied. The fatigue properties of the smooth samples were compared in a room temperature air environment. The results show that when the fatigue life of both samples reaches 5×105 cycles, the cyclic stress value of the notched sample is 52.7% lower than that of the smooth sample; As the stress decreases in the same environment, the fatigue life of the alloy increases; Under the same stress conditions, the alloy has the lowest fatigue life under salt water environment, and the tank water storage environment is next. The fatigue life of TC21 alloy is the highest under room temperature air; When the stress is low, the difference is more significant. In the corrosive environment, the ions in the solution react with the metal atoms electrochemically, which accelerates the initiation and expansion of the crack. The concentration of ions in the 3.5% NaCl aqueous solution is larger and the electrochemical reaction is more intense.