A method for preparing a conductive polymer/carbon nanotube composite nanofiltration membrane, wherein, the method comprising the following steps: CNTs are oxidized in mixed acid solution of 70 wt.% concentrated HNO 3 and concentrated H 2 SO 4 solution with 1:3 (v/v) at 40∼100 °C for 30∼120 min; then the obtained dispersion is diluted with ultrapure water and filtered; the resulting oxidized CNTs are washed and dried; after that, the oxidized CNTs are re-dispersed to form a uniform aqueous dispersion and then vacuum-filtered onto a membrane support to yield CNT membranes; finally, the prepared CNT membrane is dried at 40∼80 °C; the prepared CNT membrane is soaked in a monomer solution of the corresponding conductive polymer for 10∼30 min before draining off the excess solution; afterwards, the CNT membrane is put into an initiator solution for initiating the polymerization of monomer; after polymerizing at 0∼25 °C for 5∼30 min, the membrane is taken out and continued to react for 4∼24 h under 0∼25 °C for completing the chemical oxidative polymerization of the monomer; wherein the conductive polymer is selected from the group consisting of polyaniline, polypyrrole and polythiophene; the concentration of the conductive polymer is 0.01-0.5 M; the initiator is selected from the group consisting of ammonium persulfate, potassium dichromate, potassium iodate, ferric chloride, ferric tetrachloride, hydrogen peroxide, aluminum trichloride, manganese dioxide and benzoyl peroxide; the molar ratio of the initiator to the monomer of the corresponding conductive polymer is 1:0.5∼2; the CNT composite membrane is fully immersed into a crosslinker solution prepared by mixing glutaraldehyde and concentrated HCl; after the crosslinking for 10∼60 min, the membrane is washed well with water and dried at room temperature to obtain the conductive polymer/CNT composite NF membrane; wherein the mass percentage of glutaraldehyde in the solution is 0.5∼5% and the molar concentration of HCl is 0.1∼2 M. CNTs are oxidized in mixed acid solution of 70 wt.% concentrated HNO 3 and concentrated H 2 SO 4 solution with 1:3 (v/v) at 40∼100 °C for 30∼120 min; then the obtained dispersion is diluted with ultrapure water and filtered; the resulting oxidized CNTs are washed and dried; after that, the oxidized CNTs are re-dispersed to form a uniform aqueous dispersion and then vacuum-filtered onto a membrane support to yield CNT membranes; finally, the prepared CNT membrane is dried at 40∼80 °C; the prepared CNT membrane is soaked in a monomer solution of the corresponding conductive polymer for 10∼30 min before draining off the excess solution; afterwards, the CNT membrane is put into an initiator solution for initiating the polymerization of monomer; after polymerizing at 0∼25 °C for 5∼30 min, the membrane is taken out and continued to react for 4∼24 h under 0∼25 °C for completing the chemical oxidative polymerization of the monomer; wherein the conductive polymer is selected from the group consisting of polyaniline, polypyrrole and polythiophene; the concentration of the conductive polymer is 0.01-0.5 M; the initiator is selected from the group consisting of ammonium persulfate, potassium dichromate, potassium iodate, ferric chloride, ferric tetrachloride, hydrogen peroxide, aluminum trichloride, manganese dioxide and benzoyl peroxide; the molar ratio of the initiator to the monomer of the corresponding conductive polymer is 1:0.5∼2; the CNT composite membrane is fully immersed into a crosslinker solution prepared by mixing glutaraldehyde and concentrated HCl; after the crosslinking for 10∼60 min, the membrane is washed well with water and dried at room temperature to obtain the conductive polymer/CNT composite NF membrane; wherein the mass percentage of glutaraldehyde in the solution is 0.5∼5% and the molar concentration of HCl is 0.1∼2 M.