A method for producing a porous membrane, the method comprising the following steps (a) to (d): (a) providing a casting solution, wherein the casting solution comprises a membrane-forming polymer dissolved in a solvent system comprising 2-pyrrolidone and N-alkyl-2-pyrrolidone; (b) forming a polymer film from the casting solution provided in step (a); (c) contacting the polymer film formed in step (b) with a liquid precipitation bath, with a gaseous phase comprising a precipitation-inducing agent or with a combination thereof to induce membrane formation, thereby obtaining a porous membrane; and (d) drying the porous membrane obtained in step (c), wherein the content ratio of 2-pyrrolidone to N-alkyl-2-pyrrolidone in the solvent system is in the range of from 80% : 20% to 30% : 70%, based on mass%, and N-alkyl-2-pyrrolidone is N-propyl-2-pyrrolidone and/or N-butyl-2-pyrrolidone, wherein the membrane-forming polymer is selected from the group consisting of polyethersulfone, polysulfone, polyphenylsulfone, polyarylenesulfone, polybisphenylsulfone, cellulose acetate, polyamide and polyvinylidene fluoride, wherein the casting solution further comprises at least one additive selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone-co-poly-vinylacetate and polyethylene glycol, and wherein the solvent system does not comprise dimethyl sulfoxide. (a) providing a casting solution, wherein the casting solution comprises a membrane-forming polymer dissolved in a solvent system comprising 2-pyrrolidone and N-alkyl-2-pyrrolidone; (b) forming a polymer film from the casting solution provided in step (a); (c) contacting the polymer film formed in step (b) with a liquid precipitation bath, with a gaseous phase comprising a precipitation-inducing agent or with a combination thereof to induce membrane formation, thereby obtaining a porous membrane; and (d) drying the porous membrane obtained in step (c), wherein the content ratio of 2-pyrrolidone to N-alkyl-2-pyrrolidone in the solvent system is in the range of from 80% : 20% to 30% : 70%, based on mass%, and N-alkyl-2-pyrrolidone is N-propyl-2-pyrrolidone and/or N-butyl-2-pyrrolidone, wherein the membrane-forming polymer is selected from the group consisting of polyethersulfone, polysulfone, polyphenylsulfone, polyarylenesulfone, polybisphenylsulfone, cellulose acetate, polyamide and polyvinylidene fluoride, wherein the casting solution further comprises at least one additive selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone-co-poly-vinylacetate and polyethylene glycol, and wherein the solvent system does not comprise dimethyl sulfoxide. wherein the content ratio of 2-pyrrolidone to N-alkyl-2-pyrrolidone in the solvent system is in the range of from 80% : 20% to 30% : 70%, based on mass%, and N-alkyl-2-pyrrolidone is N-propyl-2-pyrrolidone and/or N-butyl-2-pyrrolidone, wherein the membrane-forming polymer is selected from the group consisting of polyethersulfone, polysulfone, polyphenylsulfone, polyarylenesulfone, polybisphenylsulfone, cellulose acetate, polyamide and polyvinylidene fluoride, wherein the casting solution further comprises at least one additive selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone-co-poly-vinylacetate and polyethylene glycol, and wherein the solvent system does not comprise dimethyl sulfoxide. <EOS>