The microstructure and tensile properties of Co40NiCrMo cobalt-base elastic alloy were investigated.The results show that fce structure is the crystal structure of Co40NiCrMo alloy after heat treatment and hard-drawn.The dislocation slip and twinning are the modes of plastic deformation during the hard-drawn.Twinning is the main deformation mode of Co40NiCrMo alloy after hard-drawn when more deformation is made.