CoCrNi medium entropy alloy powder was prepared by mechanical alloying, in combination with discharge plasma sintering or high vacuum sintering, the bulk was prepared. The effects of milling time and annealing on the morphology, particle size and phase structure of CoCrNi medium entropy alloy powder were studied, The microstructure and mechanical properties of the alloy blocks prepared by different sintering methods were studied. The results show that: with the extension of milling time, the particle size of each elemental powder decreases and gradually merges. After milling for 25 h, the raw powder is mainly FCC solid solution structure, with a small amount of BCC phase; In the subsequent sintering process, a small amount of BCC phase changes, and only FCC phase structure exists in the structure. The elastic modulus of the annealed sample is 6.57 GPa, which is 1.55 times of that of the vacuum sintered sample. The yield strength of the annealed sample is 279.28 MPa, which is equivalent to that of the vacuum sintered sample. The elongation of the annealed sample is 35.97%, which is significantly higher than that of the direct vacuum sintered sample; The results showed that SPS sintered bulk alloy has a yield strength of 793.72MPa, a plastic strain of 61.08%, and a Vickers hardness of 399HV. Compared with the other two sintering methods, SPS has more potential in realizing rapid low temperature sintering of HEAs.