Abstract: In order to improve properties of starch-based biodegradable plastic films, the mechanical activated starch acetate (MASA) was synthesized from mechanical activated maize starch (MAS) with activation time for 1.0 h. At the same time, the biodegradable plastic films were produced by thermal gelatinization of starch suspensions blending MASA with degree of substitution and polyvinyl alcohol (PVA). By Fourier transform infrared spectrogram (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), the microstructure, particle shape, thermal stability were studied. The mechanical properties and biodegrade ability of the MASA/PVA were investigated by comparing with those of native starch acetate (SA). The results indicated that the microstructure and particle shape changed greatly and thermal property of MASA increased compared with those of MAS and native starch. The properties of MASA/PVA were better than those of SA/PVA, and the tensile strength of the MASA/PVA with MASA (DS=0.1) was 3.56 MPa, the breaking elongation was 146.22% before soaking in water, and the absorption of water was 134.79% after 24 h. Hot water resistance properties was good, and the rate of biodegradation was 45.90% in the soil after 20 days. The mechanical activation pretreatment effectively improved the properties of biodegradable plastic films.