The invention discloses a prefabricated form of a trapezoidal hollow component and a vertical type prefabricating method. The prefabricated form comprises a bottom mould, a core mould and an outer mould, wherein the bottom mould is fixedly arranged on ground, and the upper surface of the bottom mould is horizontal; the core mould is of a similar isosceles trapezoid shaped structure; the core mouldis arranged on the upper surface of the bottom mould; the outer mould sleeves outside the core mould and is arranged on the upper surface of the bottom mould; the outer mould comprises four outer molding boards; each outer molding board comprises a steel panel close to the core mould and a truss fixedly arranged on the outer side surface of the steel panel; steel surfaces of the four outer molding boards are vertically arranged, and the side surfaces of the four outer molding boards cling to one another; the outer molding boards are detachably fixed to form the similar isosceles trapezoid shaped structure similar to the core mould; and the outer mould is superposed with the center line of the core mould, so that the steel panel, the core mould and the bottom mould define a sealed cavity with an opening in the upper surface. The trapezoid hollow component prefabricated by adopting the prefabricated form and the vertical type prefabricating method has the characteristics of being good in overturning resistance and anti-sliding stability, strong in adaptive capacity and the like while applied to hybrid dam construction.