In this paper, a mathematic model of the stress-strain hysteresis of the SMAs was set up for engineering calculation. The model could describe the characteristics of the reorientation among martensitic variants and the stress-induced martensitic transformation microscopically. Moreover, it can also describe the behaviors of the hysteresis and inner-hysteresis of the stress-strain macroscopically. An internal variable梙ysteresis element distribution function was introduced into the model to show the inner sit...