Metal foam is a class of attractive materials, which exhibits unique combinations of physical, mechanical, thermal, electrical and acoustic properties. In particular, it is light and good at absorbing energy, which makes it attractive in automotive and aerospace applications weight is critical. In this paper, the Mg alloy foam was prepared by melt foaming method by addition of calcium as thickening agent, and $TiH_2$ or $CaCO_3$ powder as blowing agent. The macrostructural observation of foamed Mg showed that the pore structures of Mg alloy foam made by $CaCO_3$ as blowing agent were much better than that of foams made by $TiH_2$ as blowing agent. In addition, this paper showed the possible reason of fabrication magnesium alloy foam in proportion to blowing agent and the porosity range was about 40 to 76% as results value.