The tension-torsion experiments at 680 ℃ on DD3 nickel-based single crystal superalloy thin-wall tube samples were conducted. Based on the microstructure characteristics of nickel-based single crystal alloy, two-phase multi-cell microscopic scale mechanical model were established. Using the bilinear follow Hill hardening model, made finite element numerical simulation of tension / torsion cyclic displacement loading on the samples. It is indicated that the sample axis showed stress relaxing behavior and inelastic deformation accumulation under high temperature asymmetric cyclic loading. The matrix phase appeared plastic deformation accumulation at first and led to low cycle fatigue damage. The numerical simulation found that the boundary stress distortion phenomenon appeared with a single cell for tension-torsion displacement loading, it is not consistent with experimental results. While using multi-cell model could avoid this phenomenon, it can better simulate stress relaxation behavior under asymmetric cyclic loading at high temperature and study stress weaken damage for single crystal alloy.