Precipitation strengthening has been proven to be a very effective method to improve the strength, especially the yield stress of alloys. In this work, uniaxial simulations were conducted on medium-entropy alloy, CrCoNi, under temperatures of 77 K and 298 K. Through precipitating Al, Fe, Cu, and Mn in the grain boundaries (GBs) of polycrystalline CoCrNi alloys, the strength and stiffness were significantly improved. Even with a low content (~0.4%) of dopant, the ultimate strength and stiffness were observed to be enhanced by 28% and 37.5%, respectively. Analysis of the deformed configurations reveals that the doped metallic ions play a role of inhibiting GBs sliding and subsequently lead to fcc to hcp phase transformation, as well as multiple inter and intra dislocations. Types of elements also exhibit an effect on the enhancement behavior due to different binding energies, which was demonstrated by the DFT calculations.