Abstract: CoCrNiCu_x(x=0, 0.4, 0.8, 1.0)medium entropy alloys with different molar ratios were prepared by using vacuum electric arc furnace, and the microstructure, phase composition and mechanical properties of CoCrNiCu_x alloys were analyzed to find out the variation pattern of the microstructure and properties with the change of Cu content. The results show that the crystal structure of CoCrNiCu₀ alloy is a single FCC phase, with the increase of Cu content, the alloy transforms from a single FCC phase to the microstructure composed of FCC1 phase and copper-rich FCC2 phase. The microstructure of the alloy is dendritic, and the formation of FCC2 phase makes the microstructure of the alloy change from bulky dendrites to fine dendrites.After adding Cu, the yield strength and yield ratio of the alloy increase from 234.1 MPa and 0.368 to 353.1 MPa and 0.715, respectively. The elongation at break decreases from 88.0%at x=0 to 30.1%at x=1.0. The microhardness of the alloy shows an increasing trend with the maximum value of 190.58 HV.