Abstract: The area below the zero-meter level of a substation contains many concealed works, including underground pipelines, grounding grids, and foundations. The traditional two-dimensional design approach has problems such as difficulty in identifying potential hazards and frequent rework during construction. Based on a 110 kV substation in Zhejiang Province, this study uses BIM and mixed reality technologies to develop a three-dimensional digital twin model covering all disciplines. It establishes a closed-loop workflow covering design, modeling, verification, optimization, and delivery. This workflow realizes the transition from delivering construction drawings alone to delivering directly usable digital assets and lays a foundation for intelligent lifecycle management of substations.