The phase stability of high entropy alloys (HEAs) is closely related to the mechanical properties and formation mechanisms of HEAs. It has been found that the stabilization of HEAs can be affected by composition variation and external stimulation. Particularly, severely deformation can lead to the phase decomposition of stable CoCrFeMnNi HEA during subsequent intermediate annealing. However, the underlying mechanisms of the deformation stimulated destabilization of HEAs have not been well understood. In this study, we systematically investigated the phase stability of HEAs subjected to plastic deformation and subsequent intermediate annealing by using the state-of-the-art Cs-corrected TEM. It was found that crystal defects, such as dislocations, twins and grain boundaries, which are generated by plastic deformation, plays a critical role in phase decomposition of HEAs. The local structure and chemical disturbance caused by the defects can leads to significant phase separation of multicomponent solid solutions stabilized by high configurational entropy.