The invention discloses an outdoor prefabricated transformer substation. By adopting a design idea of small-sized modularized prefabrication, the transformer substation is designed to be in a prefabricated assembled structure. The transformer substation comprises a civil engineering part and an electrical part. Mostly, the civil engineering part adopts prefabricated products, wherein the strip-shaped foundations of a container and a prefabricated cabinet, and the foundation of a transformer need to be prefabricated on site. Except the transformer, the electronic part adopts a container type module or a prefabricated cabinet type module, a wire inlet module adopts a box type gas insulated switchgear (GIS) module, the whole GIS module is mounted in the container or the prefabricated cabinet, the inlet wire adopts a cable, and the transformer is connected with the GIS module through an oil-gas bushing or an overhead wire. The on-site foundation prefabrication of the civil engineering part and the in-plant production debugging work of each functional module of the electrical part are simultaneously carried out, so that the construction period is greatly shortened. The outdoor prefabricated transformer substation is constructed by prefabricating and assembling modularized structures, breaks through the construction thought of a traditional transformer substation, and is high in efficiency.