According to the expression of strain energy release ratio, a triaxiality factor, an expanding factor from isotropic material to orthotropic materials, for single crystal superalloy that contains three elastic constants was defined. By using the triaxiality factor to modify strain range as a failure parameter, effects of crystallographic orientation and multiaxial loading on fatigue life can be eliminated remarkably. Applying strain energy release ratio to describe fatigue damage course of orthotropic materials and taking account of nonlinear effect of crystal anisotropy of single crystal superalloys versus fatigue damage and alternate changing characteristic of cyclic loads by introducing an orientation function and a cyclic characteristic parameter for damage force, a low cycle fatigue damage model for single crystal superalloy was proposed. The low cycle fatigue test data correlation to DD3 and CMSX-2 single crystal superalloy with the parameter by using multivariate linear regression analysis is good and the all test data fall into the factor of 2.0 and 2.5 scatter band, respectively.