The solid/gas eutectic unidirectional solidification process is a new kind of technology fabricating the lotus-type porous structure. Besides having the properties of large specific surface area, excellent sound absorption, penetrating performance etc. of traditional porous materials, the particularity of the lotus-type porous structure makes it has extraordinary mechanical and thermal properties. There is a great potential for lotus-type porous aluminum in the field of lightweight engineering and heat dissipation of chip owing to its low density, outstanding corrosion resistance and high thermal conductivity. However, the fabrication of lotus-type porous aluminum has always been more difficulty than other metals. Until porous aluminum with excellent pore structure was fabricated under very small solidification rates (0.008~0.015 mm/s) and high superheat degrees of melt (240~340 K), the proper processing parameters were recognized to be essential for the coupled growth of solid/gas phases for Al-H₂ system, especially the solidification rate. In this work, a three-dimensional time-dependent model describing the evolution of single pore was established based on the theoretical analysis of mass transfer, gas bubble nucleation, pore growth, interruption and detachment. The morphology of single pore under different solidification rates were simulated during the Gasar process by using the finite difference method for Al-H₂ system. The research reveals: coupled growth of solid/gas phases can be achieved under the solidification rates from 0.15 mm/s to 0.005 mm/s. The average pore diameter which ranges from 100 mm to 1100 mm increases with decreasing the solidification rate. The pore length also increases while the pore aspect ratio is nearly a constant about 40 with decreasing the solidification rate. The simulated average pore diameter is in good agreement with the experimental values when solidification rate equals to 0.015 mm/s, and then being slightly lower than the experimental ones with decreasing the solidification rate. The diffusion of hydrogen into the melt during the solidification process is regarded as the main reason of the discrepancy between simulated and experimental average pore diameters. The maximum value of the simulated solidification rates for coupled growth of solid/gas phases in Al-H₂ system first increases from less than 0.01 mm/s to 0.15 mm/s and then being a constant, while the minimum ones increase from about 0.0001 mm/s to 0.01 mm/s with improving the overheat degree of melt and hydrogen partial pressure. By comparing the relative parameters of Al-H₂ and Cu-H₂ systems, the solubility of hydrogen is regarded to be the main parameter which determines solidification rates of coupled growth of solid/gas phases for Al-H₂ system.