To refine the microstructure and improve the mechanical properties of AZ91D alloy by expendable pattern shell casting (EPSC), the mechanical vibration method was applied in the solidification process of the alloy. The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91D magnesium alloy were studied. The results indicated that the mechanical vibration remarkably improved the sizes, morphologies and distributions of the primary α-Mg phase and β-Mg17Al12 phase, and the densification and tensile properties of the AZ91D alloy. With an increase in amplitude, the microstructures were gradually refined, resulting in a continuous increase in mechanical properties of the AZ91D alloy. While, with the increase of pouring temperature, the microstructures were continuously coarsened, leading to an obvious decrease of the mechanical properties. The tensile strength and yield strength of the AZ91D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730 oC were 60％ and 38％ higher than those of the alloy without vibration, respectively.