Abstract: The effect of hot forging on the microstructure and mechanical properties of CoCrNi tri-principal element medium-entropy alloy were investigated by mechanical properties testing and OM, XRD, SEM and EBSD analysis. The results show that the grain of the alloy after hot forging is obviously refined, and the crystal microstructure is face-centered cubic structure（FCC）. A large number of annealing twins act together with the spreading layer, which makes the alloy have good room temperature mechanical properties. The yield strength reaches 380 MPa, the tensile strength reaches 850MPa, the elongation is up to 92%, and the alloy exhibits very high strength plasticity, the strength-plastic product is 76.5 GPa·%.