Abstract We perform molecular dynamics simulations to investigate shock-induced amorphization in CoCrNi, a medium entropy alloy (MEA) and its mean-field variant without lattice distortion. We show that a critical velocity exists above which amorphization occurs. At a low shock velocity of 800 m/s, dislocation slip and twins dominate and amorphization does not happen, but as the shock velocity increases, the deformation mechanism transitions from slip and twinning to solid-state amorphization. Under ultra-high shock velocities, extensive amorphization occurs, following the precursor of shock wave, eliminating anisotropy in spall strength. Compared to the mean-field model, lattice distortion in the MEA causes substantially more amorphization, resulting in a lower spall strength, since voids nucleate and grow preferentially in the amorphous regions.