In order to study the effect and mechanism of post-treatment on the microstructure and properties of medium entropy alloy in CoCrNi, the medium-entropy alloy in Co0.3288-Cr0.3288-Ni0.3288-Mo0.0136 was prepared by laser deposition. The microstructure and properties of medium-entropy alloy in CoCrNiMo0.0136 under laser deposition, hot forging and hot forging sandblasting were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, electron backscatter diffraction, 3-D surface profilometer, and universal tensile testing machine. The results show that the medium-entropy alloy in laser deposited CoCrNiMo0.0136 has stable face-centered cubic structure after as-deposited, hot-forging, and hot-forging sandblasting. In the deposited state, the grain size of alloy is coarse, because of microsegregation, there is a substructure with uneven distribution of elements in the grain, and the strength of the alloy is low, but the plasticity is good. After hot forging treatment, the grain size of alloy is significantly refined, and more annealing twins can be observed. Compared with the laser deposited state, the yield strength is increased by 132.88%, the tensile strength is increased by 53.78%, and the elongation has no obvious change. After the hot forging sample was sandblasted, the surface of the sample showed a gradient nanostructure with a thickness of about 100μm, and there were a large number of nano-twins in the plastic deformation layer, the yield strength and tensile strength increased by 220.09% and 96.22% respectively, and the elongation did not change significantly. Through thermoplastic processing and preparation of nano-gradient surface structure, the static properties of medium-entropy alloy in Mo-doped CoCrNi can be effectively improved.