The invention provides a waterproof fabric for side curtains of carriages and a preparation method of the waterproof fabric, and solves the technical problems that existing waterproof fabric does not have characteristics of flame retardance, ultraviolet resistance, aging resistance and the like, cannot be used in complex environments, is single in use, lacks preparation methods and the like. The waterproof fabric for the side curtains of the carriages comprises a base fabric layer, wherein protection layers are fixed on two sides of the base fabric layer, and each protection layer comprises components in parts by weight as follows: 24-36 parts of waterborne polyurethane, 1-4.5 parts of nano titanium oxide, 2-3 parts of a migration inhibitor, 2.4-3 parts of magnesium oxide, 2.2-3.4 parts of zinc oxide, 0.2-0.5 parts of an antioxidant, 2-6 parts of a crosslinking agent, 2-7 parts of a catalyst and the balance of water. The waterproof fabric has the advantages of high practicability and good product quality.