This　study　explored　a　multi-mechanism　approach　to　improving　the　mechanical　properties　of　a　CoCrFeMnNi　high-entropy　alloy　through　non-equiatomic　alloy　design　and　processing.　The　alloy　design　ensures　a　single-phase　face-centered　cubic　structure　while　lowering　the　stacking　fault　energy　to　encourage　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　peening　(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　x　10(10)　kJ/m(3),　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　microstructure　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.　(C)　2021　Published　by　Elsevier　Ltd　on　behalf　of　Chinese　Society　for　Metals.