The invention discloses a preparation method of a porous aluminum alloy, and belongs to the technical field of porous metals. The preparation method comprises the steps that firstly, preheated NaCl particles and aluminum alloy melt are subjected to liquid stirring and uniform mixing, and acquiring a salt/aluminum alloy composite blank after cooling solidification; then, heating the salt/aluminum alloy composite blank to be at the temperature in a semisolid temperature zone of the aluminum alloy, and acquiring a salt/aluminum alloy composite with a certain appearance shape and length through semisolid extrusion and shearing; and finally, removing the NaCl particles in the salt/aluminum alloy composite through a water solution, and acquiring the micron-aperture porous aluminum alloy of whichthe aperture range is 5 m to 200 m and the porosity is 40% to 70%. According to the obtained micron-aperture porous aluminum alloy, the pore structure and appearance shape are controllable, apreparation technology is simple, cost is low, and industrial production can be achieved.