Abstract: A thermodynamical constitutive model of shape memory alloy (SMA for short) under complex stress state is established based on Helmholt free energy. The thermodynamical constitutive model of an energy dissipation spring made of SMA is also established based on this model. With the Brinson抯 phase transformation equation, the development equations of inner variable about martensite percentage of the spring is given after introducing the concept of equivalent stress. A design method for the energy dissipation spring made of SMA is recommended combining the design method of common spring. The numerical calculation is carried out utilizing MATLAB program developed by the authors. The investigation result indicates that the energy dissipation spring made of SMA has better capacity of energy dissipation. The theory presented in this paper agrees preferably with the results of other researchers.