It is difficult to control the pore size and distribution of Mg alloy foam by melt foaming method using titanium hydride as blowing agent and extraordinary coarse pore structures is often found in the Mg alloy foams. Using CaCO3 instead of titanium hydride as blowing agent, AZ31 Mg alloy foams with small well structure, porosity 35.0~72.0 % and average pore size 0.04~0.16 cm could successfully be fabricated In this study; AZ31 Mg alloy foam with the holding time of 30s had the best energy absorption. The energy absorption value of AZ31Mg foam was 5.52MJ/m3. After that, AZ31 foams sample was polished and rusted. The thickness cells were analyzed by use of Metallurgical Microscope and software. Then SEM micrograph of AZ31 Mg alloy foam and EDS analysis of the cell wall.