Abstract: In this work, the single phase face-centered-cubic (FCC) CoCrNi medium entropy alloy (MEA) is prepared by combining low-temperature rolling and annealing below recrystallized temperature. The alloy annealed at low temperature obtains ultra-high yield strength of 1 490 MPa, which is 31.3% higher than that of the alloy low-temperature rolled. On one hand, low-temperature rolling limits the dynamic response and maintain high dislocation density. On the other hand, annealing below recrystallized temperature causes the dislocation rearrangement of the alloy, promotes the formation of dislocation unit of high density and stacking fault, and leads to the formation of a small amount of nanocrystals and ultra-fine crystals.