The tensile behavior of γ-TiAl alloys with vacancy defects has been studied by molecular dynamics simulation (MD) considering different lattice orientation. A succession of simulations were performed to analyze the effect of vacancy and lattice orientation on mechanical properties and micro-defect evolution. The results indicate that the orientation has evidently impacts on critical stress with Ti and Al vacancy. The yield stress of the model with Ti vacancy is higher than containing Al vacancy model along three crystal directions. During the deformation of single crystal γ-TiAl alloys, it is found that the dislocation density has the same changeable trend as the number of stacking faults. In addition, the influence of temperature on yield strength also was discussed. When the temperature increases, the ultimate stress declines non-linearly, and elastic modulus of the material decrease obviously. The higher temperature, the less influence of crystal orientation and vacancy defect on the ultimate stress.