A new class of metallic materials based on multi-principal elements at equiatomic proportion called high-entropy alloys (HEAs) presents excellent mechanical properties over a wide range of temperatures and strain rates. Some HEAs demonstrated higher strain rate sensitivity compared to other metallic materials at both quasi-static and high strain rate deformation. However, most of the researches on high strain-rate deformation focused on mechanical behavior and little attention has been given to detailed microstructural evolution including texture, shear banding or chemical fluctuation induced by adiabatic heating. In this research, high strain rate compression test was done at 15,000 s-1 on a prototypical CrMnFeCoNi HEA and the microstructural evolution was characterized using electron back-scattered diffraction and transmission electron microscopy (TEM). It was found that deformation induced strong <110> fiber texture formed along the compression direction. Several adiabatic shear bands with thicknesses of ~20 µm formed near the edge of the sample. In addition, significant compositional fluctuation of Mn and Ni element has been observed in the shear band and shear flow zones. Vickers micro-indentation along those compositional fluctuation shown the local hardness variation in MnNi enriched and depleted area as well as in the shear band. Detailed microstructural analysis reveals how stacking fault energy variation, which is caused by the composition variation, affects local grain morphology and hardness distribution. The deformation mechanism that leads to change local mechanical properties will be discussed based on the structural characterization results.