Abstract: The relationship between the dynamic mechanical properties and microstructure of fine-grained magnesium alloy are investigated. The deformation mechanism is analyzed. The quasi-static properties under compression are investigated too. It is found that the alloy possesses high dynamic strength yet low quasi-static compression strength, It has high dynamic strength as a result of the rate of strain. While only a small quantity of thin twins are found in the deformation microstructure of fine-grained magnesium under dynamic loading, slippage is the main deformation mechanism of the ductility deformation under dynamic loading.