To overcome these shortcomings of the blowing agent, which is used too much as the foaming agent for fabricating aluminum foams in melt foaming processing, as high cost, poor dispersion, difficult to match the foaming process and degrade the performance of the material, a new vacuum foaming processing was employed to prepare AlSi12 alloy foams. The processes that related to the initial pores and the cell structure of the vacuum foamed AlSi12 foams were studied. The results showed that: (1) Well-distribution, fine initial pores were obtained by the processing parameters: melting AlSi12 alloy at 620℃ for 1h, adding 1%SiC and 2% Ca into the melt and stirring the melt for 10min with stirring speed 2000r/mm to increasing the melt viscosity, then adding a few of TiH2 (0.02%) into the melt and stirring the melt for 6min with stirring speed 2000r/min; (2) AlSi12 alloy foams with uniform cell structure, average pore diameter 2.4mm and porosity 83.7% were obtained by the vacuum foaming processing: foaming the melt for 10s with vacuum degree of 5Pa, and cooling the melt foams for 6min in vacuum surroundings; (3) The bobble nucleation of the initial pores in the AlSi12 alloy melt were heterogeneous nucleation, and these phases, SiC, Al2O3, SiO2, etc., acted as the nuclei of the heterogeneous nucleation.