NOVELTY - Composite fiber membrane with unidirectional permeable property comprises two layers, which have hydrophilic- hydrophobic difference, and are closely and seamlessly connected. The hydrophilic layer is nanoscale fiber membrane, which is composed of hydrophilic polymer A, and comprises randomly arranged nanoscale fiber. The hydrophobic layer is micron-scale fiber membrane, which is composed of hydrophobic polymer B, and comprises randomly arranged micron-scale fiber. The polymer A is polyvinyl alcohol, cellulose acetate, or polyacrylate. The polymer B is e.g. polyurethane or polystyrene.    USE - Composite fiber membrane with unidirectional permeable property used in perspiration waterproof cloth, fuel cell electrolyte membrane, and unidirectional liquid transport and separation fields.    ADVANTAGE - The composite fiber membrane has excellent unidirectional permeable property, hydrophilic/hydrophobic difference, simple production, low energy consumption, and high efficiency.    DETAILED DESCRIPTION - Composite fiber membrane with unidirectional permeable property comprises two layers, which have hydrophilic- hydrophobic difference, and are closely and seamlessly connected. The hydrophilic layer is nanoscale fiber membrane, which is composed of hydrophilic polymer A, and comprises randomly arranged nanoscale fiber. The hydrophobic layer is micron-scale fiber membrane, which is composed of hydrophobic polymer B, and comprises randomly arranged micron-scale fiber. The polymer A is polyvinyl alcohol, cellulose acetate, or polyacrylate. The polymer B is polyurethane, polystyrene, poly(methylmethacrylate), or polycaprolactone. An INDEPENDENT CLAIM is included for preparation of composite fiber membrane with unidirectional permeable property comprising:    (A) preparing spinning solution by dissolving pure polymer A in solvent A i.e. water, analytically pure acetone, or anhydrous ethanol at 20-25 degrees C; fully stirring until completely dissolving the polymer A; obtaining 10-30 mass% polymer A electrostatic spinning solution; dissolving pure polymer B in solvent B i.e. one or two of analytically pure N,N-dimethylformamide, analytically pure tetrahydrofuran, or analytically pure trichloromethane at 20-25 degrees C; fully stirring until completely dissolving the polymer B; and obtaining 10-35 mass% polymer B electrostatic spinning solution, where when polymer A is polyvinyl alcohol, glutaraldehyde needs to be added to solvent A at first when preparing polyvinyl alcohol electrostatic spinning solution, and then polyvinyl alcohol is dissolved in the mixture of glutaraldehyde and solvent A, where mass ratio of glutaraldehyde to polyvinyl alcohol in polymer A spinning solution is 1:3-1:2;    (B) placing the polymer A electric spinning solution in a syringe of electrostatic spinning device; forcing high voltage electrostatic field between the metal nozzle of syringe and receiving substrate, where high voltage electrostatic field has a voltage of 10-35 kV; regulating the distance of metal nozzle and receiving substrate at 10-30 cm; forcing high voltage electrostatic field to make the polymer A electric spinning solution produce jet; obtaining randomly arranged nanoscale fiber membrane on the receiving substrate, where thickness of nanoscale fiber membrane is 25-35 mu m; and uniformly covering the fiber membrane on the receiving substrate; and    (C) placing the polymer B electric spinning solution to the other clean syringe of electrostatic spinning device; taking the polymer A nanoscale fiber membrane as the receiving substrate; forcing high voltage electrostatic field having voltage of 1-25 kV between the metal nozzle of syringe and the receiving substrate; regulating the distance of the metal nozzle and receiving substrate at 10-25 cm; uniformly covering the formed micro-scale fiber membrane on the surface of the receiving substrate, which is composed of nanoscale fiber membrane of polymer A; and forming randomly arranged micron-scale fiber membrane of polymer B on the substrate of nanoscale fiber membrane, where the thickness of micron-scale fiber membrane is 1.0-3.0 mu m.