The mechanical characteristics during superplastic deformation of 7 B04 aluminum alloy were investigated by high temperature tensile test, and the microstructure evolution of superplastic deformation was observed by optical microscopy, scanning electron microscopy, electron backs cattered diffraction, transmission electron microscopy and focused ion beams. The results indicate that optimal deformation condition is at 515 ℃ and 3×10^-4 s^-1, where the elongation rate reaches the maximum value of 850%.At the initial stage of deformation, voids are gradually generated under the combined action of vacancy migration and tensile stress. Partial grains are fractured along the tensile direction, resulting in a slight decrease in grain size along the tensile direction and a decrease in grain aspect ratio, and the grains grow gradually with the increase of strain subsequently. With the proceeding of deformation, stripe bands appear on the surface due to the joint action of diffusion creep and grain boundary sliding, and precipitate free zones are formed near grain boundaries. The absence of intracrystalline dislocation slip is achieved, and the superplastic deformation mechanism is characterized by grain boundary sliding accompanied with diffusion creep.