The invention discloses a multifunctional diaphragm of a lithium-sulfur battery, which comprises a diaphragm substrate, wherein at least one surface of the diaphragm substrate is coated with a modified coating, the modified coating is a composite coating containing polydopamine, a carbon material and a catalytic material, and a catalyst is one or more of metal sulfide, metal carbide and metal oxide. The preparation method comprises the steps of firstly preparing a polydopamine/carbon dispersion liquid, then uniformly mixing the polydopamine/carbon dispersion liquid with the catalytic material, the thickening agent and other assistants to prepare slurry, finally coating the surface of the diaphragm matrix with the slurry, and drying to obtain the multifunctional diaphragm of the lithium-sulfur battery. The lithium-sulfur battery diaphragm prepared by the invention has shuttling inhibition and catalytic conversion functions on polysulfide, oxygen-containing functional groups in a polydopamine molecular chain inhibit shuttling of the polysulfide, the polysulfide is adsorbed on the coating side of the diaphragm under the action of the catalytic material and the carbon material, and polysulfide is prevented from shuttling to the negative electrode through the inhibition-conversion effect, so that the cycle life of the lithium-sulfur battery is remarkably prolonged.