The invention provides a foaming device for a porous magnesium alloy. The foaming device comprises a melting furnace, a furnace cover, a liquid shifting spoon, a foaming mould and a stirrer, wherein the furnace cover is arranged at the top of the melting furnace and provided with a first through hole and a second through hole; the liquid shifting spoon penetrates through the first through hole; the foaming mould is fixed to the second through hole and hung in air of the interior of the melting furnace; and the stirrer is arranged in the foaming mould. According to the foaming device for the porous magnesium alloy, short process foaming can be achieved, the steps of adding a tackifier and thermal insulation foaming are omitted, stirring for a long time is not conducted in a semi-solid state, on the one hand, existing alloy components cannot be changed, the impact on product performance is small, on the other hand, a foaming technology is made to be suitable for most of magnesium alloysand good in forming, and then on the one hand, the foaming time is shortened, and the foaming efficiency is improved; and through structural design of the melting furnace and the foaming mould, the decomposing speed of a foaming agent can be made be matched with the temperature decreasing and tackifing speed of a magnesium alloy liquid, so that polymerization and overflowing of precipitated bubbles are prevented, and the obtained porous magnesium alloy is small and even in hole diameter.