The superplastic deformation mechanism of Mg-7.0Al-0.4Zn alloy was studied by EBSD technology. Results indicate that with increasing of strain amount, the texture of {0002}//ED is strengthened obviously, and intragranular sliding plays a main role during the accommodated deformation. Twins have started at the medium and the final deformation stages; when approaching to failure, intragranular sliding vanishes, and twins replace it to play a main role. But the contribution of twins to deformation is relatively small