This study explored a multi-mechanism approach to improving the mechanical properties of a CoCr-FeMnNi high-entropy alloy through non-equiatomic alloy design and processing.The alloy design en-sures a single-phase face-centered cubic structure while lowering the stacking fault energy to encour-age the formation of deformation twins and stacking faults by altering the equiatomic composition of the alloy.The processing strategy applied helped create a hierarchical grain size gradient microstructure with a high nanotwins population.This was achieved by means of rotationally accelerated shot peen-ing(RASP).The non-equiatomic CoCrFeMnNi high-entropy alloy achieved a yield strength of 750 MPa,a tensile strength of 1050 MPa,and tensile uniform elongation of 27.5％.The toughness of the alloy was 2.53×1010 kJ/m3,which is about 2 times that of the same alloy without the RASP treatment.The strength increase is attributed to the effects of grain boundary strengthening,dislocation strengthening,twin strengthening,and hetero-deformation strengthening associated with the heterogeneous microstruc-ture of the alloy.The concurrent occurrence of the multiple deformation mechanisms,i.e.,dislocation deformation,twining deformation and microband deformation,contributes to achieving a suitable strain hardening of the alloy that helps to prevent early necking and to assure steady plastic deformation for high toughness.