In this paper, the high temperature mechanical properties and the associated deformation mechanism of CoCrNi-based entropy alloy with rich-CoCr content were studied. It is found that the alloy with the compostions of Co_33.3Cr_30.6Ni_26.1Al₅Ti₅ (at. %) exhibited excellent instantaneous tensile properties in the temperature range of 600℃ to 800℃ after hot forging and aging heat treatment. In particular, the yield strength anomaly occurs at 700℃, the tensile yield strength is as high as 944 MPa and the elongation at break is 16%, which is better than most nickel-base and nickel-cobalt-base superalloys. By means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and three-dimensional atomic probe (3D-APT), it is found that the strong ordered strengthening of high-volume fraction multi-principal γ" [(Ni, Co, Cr)₃(Al, Ti)] phase combined with grain boundary strengthening aring from the formation of FCC phase with rich-CoCr is the main factor for the excellent high temperature properties of the alloy.