The invention discloses a preparation method of an electrostatic spinning fiber composite fin. The preparation method includes: (1), well mixing ion exchange resin, a volatile solvent and a hygroscopic material to preparing spinning liquid, wherein mass fraction of the ion exchange resin is 9-20%, and mass fraction of the hygroscopic material is smaller than or equal to 2%; (2), pouring the spinning liquid into an injector of an electrostatic spinning device for electrostatic spinning, and putting a nanofiber membrane obtained by electrostatic spinning onto a fin; (3), putting the fin in an oven for drying to obtain the electrostatic spinning fiber composite fin. Electrostatic spinning technology is utilized to directly perform electrostatic spinning on the surface of the heat exchanger fin to prepare an ion exchange resin electrostatic spinning nanofiber layer; compared with conventional hygroscopic resin paint, the electrostatic spinning nanofiber layer has more ideal specific surface area, hygroscopic rate and hygroscopic ability can be improved effectively, so that dehumidifying performance of the fin is improved effectively.