A door made of polyurethane, including a door body, the door body including a plurality of integrated plates stacked on one another for supporting. A method for preparing the door includes providing a mold, and spraying a parting agent inside the mold; heating the mold to a temperature of 30-70° C., spraying the parting agent, and placing a plurality of plates or a metal skeleton in the mold; mixing raw materials to obtain a mixture; injecting the mixture into the mold to cover the stacked plates, and curing for 30-90 min; demolding, transferring a product from the mold to a thermostatic chamber for shaping at a constant temperature; trimming uneven edges and surfaces of the product; and spraying a paint on the product.