Lotus-type porous Mg-Zn alloys were fabricated successfully by Bridgman-type directional solidification method. The pore structure and porosity of Mg alloys at different Zn content and hydrogen pressure were studied. The porosity of Mg-1wt.% Zn was predicted through the theoretical calculation. The results show that pore structure can be influenced by the addition of Zn element. As the content of Zn increases from 0 to 2 wt.%, average pore diameter increases. The porosity of Mg-1wt.%Zn alloy clearly decreases with the increasing of the hydrogen pressure from 0.1MPa to 0.6MPa. Based on a model for estimating the solubility of hydrogen in multi-component molten metals, the calculated results of porosity at the solidification stage (20mm height) with a changed hydrogen pressure in Mg-1wt.%Zn alloy, are in good agreement with the experimental results. Through observations on the microstructures, the column grains of Mg-Zn alloy are changed into equiaxed grains as the content of Zn increases. Also, the formation of pore at different solidification stages was studied, which can supply theoretical basis for the fabrication of Gasar Mg-Zn alloy in the biological applications.