Abstract: Fatigue tests were conducted on domestically produced Inconel 690 nickel-based alloy in room temperature air, room temperature water, and 350 °C high temperature air environments under conditions of the loading frequency of 20 kHz, the stress ratio of −1, and the stress amplitude ranging from 305 MPa to 350 MPa. The ultra-high cycle fatigue life and fatigue fracture characteristics of the alloy in different environments were studied. The results show that Inconel 690 nickel-based alloy had ultrahigh cycle fatigue failure in different environments. At the same stress amplitude, the fatigue life was the highest in room temperature air environment, followed by in the room temperature water environment, and the fatigue life was the lowest in high temperature air environment. The fracture mode of the alloy in all environments was cleavage fracture. In room temperature air environment, the high-cycle fatigue failure modes of the alloy included internal fatigue failure and surface fatigue failure with single crack initiation. In room temperature water environment, due to the effect of the mild corrosivity of water and cyclic loading, surface fatigue failure of the alloy occurred with either single or multiple crack sources. In high temperature air environment, due to the alloy strength reduction and surface oxidation, surface fatigue failure occurred with single crack initiation.