Abstract: Urban central areas feature land shortage and intensive power load, making conventional indoor and outdoor substations unable to match urban grid upgrading demands. Semi-underground substations effectively resolve difficulties in deploying high-voltage facilities in downtown zones. No domestic practical projects of 330kV semi-underground substations have been constructed so far, lacking mature design criteria for its distribution devices. Taking a planned 330kV semi-underground substation in Northwest urban area as the research object, this paper optimizes main electrical connections and equipment layout under limited underground space. For the layout with 3 outgoing circuits and 3 main transformers, the breaker-and-a-half scheme achieves higher reliability and better economic performance than the double-bus double-segmented scheme. Linear arrangement of 330kV GIS cuts indoor width by2-3m relative to Z-type layout; the recommended net width of 15.0m meets installation and overhaul demands. Combined verification of hoisting space and safety clearance for voltage withstand tests sets the GIS chamber net height to 14.5m. This integrated optimized scheme balances wiring configuration, spatial size and test safety, and can serve as design references for similar projects.