The invention discloses a preparation method of a multilayer sandwich type electrostatic-spinning polymer nanofiber composite membrane. The preparation method comprises the steps of firstly, spinning a polymer spinning liquid into a fiber membrane in an electrostatic manner, then spraying a spraying liquid containing inorganic nano-particles to the surface of the electrostatic-spinning fiber membrane by virtue of a jetting technique, continuously spinning the fiber membrane, and repeatedly carrying out the steps according to specific conditions so as to prepare the multilayer sandwich type composite membrane. As the inorganic nano-particles are adhered to the surface of the fiber membrane, not only can the ultrahigh specific area and the specific structural advantage of a nanofiber be brought into full play, but also the selectable ranges of the spraying liquid and the polymer spinning liquid are flexible, so that spraying liquids containing different inorganic nano-particles can be sprayed to electrostatic-spinning fiber membranes made from different raw materials according to actual demands so as to prepare sandwich type composite membranes with different functions, stable structures and good properties, and the application range of the electrostatic-spinning polymer nanofiber composite membranes is expanded.