It has been experimentally proved that strain hardening exponent has very strong sensitivity to structure. The measuring result of precise experiment indicated that the variational laws of nυ (the strain hardening exponent under constant velocity), n (under constant strain rate) and np (under constant load) with ε strain are entirely different. Considering the structure sensitivity in superplasticity and plasticity (which means that the strain hardening exponent is related to strain as well as strain rate), this paper deduces the analytical expressions for nυ,n and np from the state equation. Thus, the mechanical essence of nυ,n and np corresponding the change of ε is revealed. And the experimental results on typical material Zn 5%Al are interpreted successfully which show reliability of the theory.