With scanning electron microscope (SEM), the surface morphology of phase boundary sliding (PBS) in superplastic deformation (SPD) of Zn-Al alloy and the diffusion behavior of Zn, Al interfaces in their powers sintering have been investigated. The results show that Zn-Al eutectoid microstructure can be achieved through their powders sintering, and the diffusion characteristic between Zn and Al is just a demonstration of Kirkendall effect, in which Zn can dissolve into Al whereas A1 can hardly dissolve into Zn. During sintering, a diffusion-solution zone ?′ has formed and subsequently transformed into a eutectoid microstructure in the cooling process. The superplastic deformation mechanism of Zn-Al eutectic alloy is phase boundary sliding which is controlled by the diffusion-solution zone ?′. If the diffusion-solution zone ?′ is unsaturated, it will have much more crystal defects and the combination between ?′ and phase ? is weak, thus the process of phase boundary sliding becomes easily; on the contrary, if the diffusion-solution zone ?′ becomes thick and saturated, the sliding will be difficult.