The invention discloses waterproof rain cloth for automobiles and a preparation method and belongs to the technical field of waterproof materials of the automobiles. The waterproof rain cloth comprises a padding layer and a waterproof and anti-corrosion layer on the upper surface of the padding layer, wherein the waterproof and anti-corrosion layer is a graphene modified polyurethane coating; a light reflecting layer, namely, an aluminized PE (polyethylene) layer is arranged on the upper surface of the waterproof and anti-corrosion layer; an elastic buffer layer, namely, a polyurethane foam layer, is arranged on the lower surface of the padding layer; a tough waterproof layer, namely, a titanium dioxide/graphene/natural rubber nanocomposite layer, is arranged on the lower surface of the elastic buffer layer; the padding layer and the elastic buffer layer are connected through a bonding layer, namely, a graphenemodified epoxy resin bonding agent, and the tough waterproof layer and the elastic buffer layer are connected through the bonding layer. The preparation method comprises steps as follows: composites of all layers are prepared firstly, and the padding layer is coated and boned withthe prepared composite of each layer. The waterproof rain cloth has better waterproof and anti-corrosion effects and better elasticity and toughness, the preparation method adopts a simple process and mild conditions, and the waterproof rain cloth and the preparation method have better application prospect.