rCoNi-based medium- or high-entropy alloys with low stacking fault energy have excellent fracture toughness at room temperature or low temperature. Moreover, under impact conditions, the variety of deformation mechanisms imparts excellent deformation ability to CrCoNi-based medium- or high-entropy alloys, which can be used as impact-resistant structural materials in extreme environments. However, the dilemma of "strength-plasticity" in metallic materials is still observed in CrCoNi-based medium- or high-entropy alloys, and the low yield strength limits the potential application of CrCoNi-based medium- or high-entropy alloys. Therefore, selecting appropriate strengthening methods to improve the yield strength of CrCoNi-based medium- or high-entropy alloys while maintaining their high plasticity has become a hotspot in the research of high-entropy alloys at present. This article introduced the strengthening methods  currently applied in CrCoNi-based medium- or high-entropy alloys from three aspects: solid element, lattice defects, and phase structure. Various strengthening and toughening mechanisms, such as solid solution elements, interstitial atoms, dislocations, twinning, phase transformations, and gradient structures, were reviewed. By learning from the deformation mechanisms of CrCoNi-based medium- or high-entropy alloys, the different strengthening mechanisms and their impact on the increase in mechanical properties were analysed, providing ideas for the design of high-strength and high-toughness alloys with low stacking fault energy.