A method of preparing a porous membrane, comprising: (a) synthesizing a hierarchically structured porous support by coating ceramic particles on one side of a ceramic support to fill the pores of the porous support and control the pore size of the porous support; and (b) synthesizing a membrane by forming zeolitic imidazolate frameworks (ZIFs) inside the hierarchically structured porous support by performing counter diffusion; wherein the hierarchically structured porous support has pores of 2 to 10 nm and the ceramic support has pores of 50 to 1000 nm; and wherein the pore size distributions are obtained by using an automatic mercury porosimeter; and wherein step (b) comprises adsorbing Zn 2+ or Co 2+ on the porous support by immersing the hierarchically structured porous support synthesized in the step of (a) in a zinc salt solution or a cobalt salt solution, and then forming Zn 2+ or Co 2+ imidazole crystals inside the porous support by immersing the porous support adsorbed with Zn 2+ or Co 2+ in an imidazole solution; and wherein the zinc salt solution, the cobalt salt solution, or the imidazole solution is dissolved in at least one solvent selected from the group consisting of methanol, ethanol, propanol, iso-propanol, tert-butanol, n-butanol, methoxyethanol, ethoxyethanol and distilled water; and wherein the porous membrane has a thickness of 0.1 to 500 μm; and wherein the ceramic particles in the step of (a) are at least one selected from the group consisting of α-alumina, γ-alumina, silica, glass, mullite, zirconia, titania, yttria, ceria, vanadia, calcium oxide, phosphor oxide and mixtures thereof. (a) synthesizing a hierarchically structured porous support by coating ceramic particles on one side of a ceramic support to fill the pores of the porous support and control the pore size of the porous support; and (b) synthesizing a membrane by forming zeolitic imidazolate frameworks (ZIFs) inside the hierarchically structured porous support by performing counter diffusion; wherein the hierarchically structured porous support has pores of 2 to 10 nm and the ceramic support has pores of 50 to 1000 nm; and wherein the pore size distributions are obtained by using an automatic mercury porosimeter; and wherein step (b) comprises adsorbing Zn 2+ or Co 2+ on the porous support by immersing the hierarchically structured porous support synthesized in the step of (a) in a zinc salt solution or a cobalt salt solution, and then forming Zn 2+ or Co 2+ imidazole crystals inside the porous support by immersing the porous support adsorbed with Zn 2+ or Co 2+ in an imidazole solution; and wherein the zinc salt solution, the cobalt salt solution, or the imidazole solution is dissolved in at least one solvent selected from the group consisting of methanol, ethanol, propanol, iso-propanol, tert-butanol, n-butanol, methoxyethanol, ethoxyethanol and distilled water; and wherein the porous membrane has a thickness of 0.1 to 500 μm; and wherein the ceramic particles in the step of (a) are at least one selected from the group consisting of α-alumina, γ-alumina, silica, glass, mullite, zirconia, titania, yttria, ceria, vanadia, calcium oxide, phosphor oxide and mixtures thereof. wherein the hierarchically structured porous support has pores of 2 to 10 nm and the ceramic support has pores of 50 to 1000 nm; and wherein the pore size distributions are obtained by using an automatic mercury porosimeter; and wherein step (b) comprises adsorbing Zn 2+ or Co 2+ on the porous support by immersing the hierarchically structured porous support synthesized in the step of (a) in a zinc salt solution or a cobalt salt solution, and then forming Zn 2+ or Co 2+ imidazole crystals inside the porous support by immersing the porous support adsorbed with Zn 2+ or Co 2+ in an imidazole solution; and wherein the zinc salt solution, the cobalt salt solution, or the imidazole solution is dissolved in at least one solvent selected from the group consisting of methanol, ethanol, propanol, iso-propanol, tert-butanol, n-butanol, methoxyethanol, ethoxyethanol and distilled water; and wherein the porous membrane has a thickness of 0.1 to 500 μm; and wherein the ceramic particles in the step of (a) are at least one selected from the group consisting of α-alumina, γ-alumina, silica, glass, mullite, zirconia, titania, yttria, ceria, vanadia, calcium oxide, phosphor oxide and mixtures thereof.