Abstract: The construction mode of substations is changing to modular design and assembly construction. As an important facility for distributing electrical energy, substations in settlement-sensitive areas generally adopt cast-in-place concrete overhead structures, and their indoor electrical equipment is installed on the cast-in-place concrete overhead structure. The cast-in-place concrete overhead structure can no longer meet the requirements of "standardized design, factory processing and assembly construction" of substations. The paper proposed a new composite overhead structure system that could be used as a foundation for indoor electrical equipment in substation distribution rooms. The structure system consists of modular longitudinal beams, cross beams, columns, panels, and other components, except for the cross beams which are made of steel, other components are made of molded and pultruded composite materials, which have the advantages of the short construction period, convenient hole opening and easy renewal and transformation. The overall scheme and design of the new structural system were systematically introduced in the paper, and the feasibility of the project under actual loading conditions was initially demonstrated.