Abstract: The present disclosure belongs to the field of preparation of high-performance alloy materials, and specifically relates to a plastic CoCrNi-based medium-entropy alloy with 2.0 GPa-level ultra-high yield strength and a preparation method thereof. The alloy is prepared by melting and casting, homogenization treatment, solution heat treatment, cold deformation and aging heat treatment. After cold deformation and aging heat treatment, the prepared alloy has a dual heterogeneous microstructure due to the discontinuous precipitation of the strengthening phase and the incomplete recrystallization composition. The CoCrNi-based medium-entropy alloy of the present disclosure has ultra-high yield strength (2.