The invention relates to a waterproof breathable film preparation method which comprises the following steps: adding poly-L-
lactic acid into a first
solvent to obtain a first solution, and adding
polypropylene glycol butyral and a pore-
foaming agent into the first solution to obtain a first
spinning solution; adding poly (beta-hydroxybutyrate) and
polyvinyl alcohol into a second
solvent to obtain a second solution; octadecanethiol and tetramethyl tetravinyl cyclosiloxane are added into the second solution, and a second
spinning solution is obtained; adding polyoxyethylene into a third
solvent to obtain a third solution; adding an inorganic non-metallic material and a hydrophobic functional material into the third solution to obtain a third
spinning solution; preparing a three-layer
nanofiber membrane from the first spinning solution, the second spinning solution and the third spinning solution through an electrostatic spinning method; carrying out cross-linking reaction on the three-layer
nanofiber membrane by using
ethylene glycol
diglycidyl ether steam, and washing by using
distilled water to obtain the waterproof breathable membrane. According to the invention, the additive and the
polymer are regulated and controlled, so that the structural performance of the film is better.