Supported ionic liquid membranes (SILMs) based on homemade asymmetric gamma-Al2O3 membranes and [BMIM] [BF4]/[BMIM][Ac] were prepared using supercritical fluid deposition (SCFD). Most of the micro- and me in the top layer of supports were blocked by ILs, while the macro-pores in the substrate (alpha-Al2O3) were partly filled. The [BMIM] [BF4]-SILMs exhibited CO2 permeance (Pa-CO2) of similar to 1.5 GPU and CO2/N-2 selectivity (alpha(CO2/N2)) of similar to 43.0, while the [BMIM] [Ac]-SILMs exhibited Pa-CO2 of similar to 0.7 GPU and alpha(CO2/N2) of similar to 44.0. It was found that deposition time, IL and co-solvent amount can influence the deposition process significantly. It was also found that the gas permeance decreased first and then maintained stable as deposition time or IL amount increased, but the SILM performance increased first and then decreased as the co-solvent amount increased. At last, the formation process of the liquid membrane was discussed by analyzing the phase behavior of scCO(2)-ethanol-IL systems.