The invention relates to a waterproof rolled material, in particular to a modified chlorinated polyethylene waterproof rolled material and a preparation method thereof, which solve the problems that the traditional waterproof rolled material can not completely satisfy each performance index of a product and the formula cost is overhigh. The waterproof rolled material is prepared from an ethylene-octylene copolymer, chlorinated polyethylene, linear high-pressure polyethylene, a filler intensifier, a softener plasticizer, a phenol antioxidant, a heat stabilizer, a lubricant and a light stabilizer, and the preparation method thereof comprises the following steps: mixing and stirring various raw materials; granulating by sequentially adopting a plastic refining machine, a double-roll machine and a grain cutting machine; adding grain materials into a single-screw extruding machine for extrusion and molding through a mould; and adding the molded material into a three-roll cooling embossing machine for rolling to obtain the waterproof rolled material. Not only the peculiar softness, the elongation percentage and the rebound resilience of rubber are reserved, but also the higher breaking tensile strength of an LLDPE is reserved, the integral sheet material has good softness, flatness and evenness, the performance index exceeds a national standard and the related standard of a railway ministry, all the ageing-resistant performance, the physical performance and the processing performance are more excellent, and the production cost is low.