Abstract: Using split Hopkinson Bar technology, for the cylindrical specimens made by the different orientation of forged ZK61 magnesium alloy, dynamic compression test have been conducted and the dynamic mechanical behavioral anisotropy and deformation mechanism have been investigated by combining the mechanical response with micro-analysis method. The results show that the transverse direction (TD) and the normal direction (ND) of the forged ZK61 magnesium alloy has few anisotropic characteristic of the dynamic mechanical behavior, while the rolling direction (RD) have conspicuous anisotropic characteristic of the dynamic mechanical behavior comparing with TD and ND. With the increase of strain rate, the change of the number of twins in different orientation specimens is different. The increase of numbers of the twins in ND specimen is the fastest and the slowest in RD specimen, while twins in TD specimen increases rapidly at first and then decreases significantly. The different plastic deformation mechanisms in the different orientations specimens results in the anisotropy of the dynamic mechanical behavior in the ZK61 magnesium alloy specimens.