The invention discloses a through roof building construction for a GIS chamber of a transformer substation. A clearance is arranged at a coupling section of a roof profiled steel plate and a through roof upright column, a water catchment and diversion trench is arranged in a lower position corresponding to the clearance, an inverted V-shaped splitter plate is arranged in an inflow direction adjacent to the through roof upright column, a clearance is arranged at the coupling section and used as a drainage gallery for little rainwater, and the rainwater is collected by the lower water catchment and diversion trench and directly drained into a rain gutter. The invention adopts the scheme of giving priority to dredging and draining and taking plugging prevention as the auxiliary method, the water catchment and diversion trench is positioned below the roof profiled steel plate, through roof steel members are arranged all around, so that rain (snow) water in the weak region of the coupling section is ensured to be drained in time, and the purposes of construction simplification and safe and lasting waterproofing are achieved.