Abstract: In order to improve the degradation reaction activity of microorganisms of maize starch, maize starch was mechanically activated by a stirring-type ball mill, using distillers yeast as the biodegradation reagent, maize starch with 60 minutes of activation time and native starch was degraded. The effects were investigated that gelatinization temperature, pH value, starch concentration, degradation time, degradation temperature and microorganisms fluids dosage influenced on degradation reaction of microorganisms from maize starch, using dextrose equivalent (DE) of the hydrolysis product of starch acetate as evaluating parameter. The morphology of the degrade process of maize starch with mechanical activated was investigated by scanning electron microscope(SEM). The results indicated that the DE increased with mechanical activation, and the maize starch with mechanical activated can be directly biodegradation without a gelatinization. The DE was 36.76% after biodegradation for 60 min, comparing with non-activated maize starch, and the DE increased by 27.80%. Mechanical activation greatly increased degradation reaction activity of microorganisms of maize starch. It indicated that the crystal structure and compact granule surface of maize starch were destroyed by mechanical activation.