Abstract: The “in-situ” electron back scatter diffraction (EBSD) experiments were carried out on the annealed pressure vessel steel 16MnR at different fatigue cycles in order to obtain the corresponding crystal orientation maps. Kernel average misorientation (KAM) value and diversification qualitatively described plastic deformation in the process of fatigue damage. The results showed that it was not inerratic linear relationship between the fatigue cycles and plastic deformation of material, but there was fatigue hardening in the fatigue process that caused material deformation rate becoming slow. Plastic deformation features showed that the grain boundaries and uneven microstructure sections were plastic deformation sensitive areas.