The invention discloses a substation GIS current transformer secondary flooding box. The substation GIS current transformer secondary flooding box comprises an expansion box which can be hoisted on the bottom surface of a CT junction box, the expansion box is a box body structure with an opening at the top and a box door of the expansion box at the front surface, the expansion box is internally provided with a horizontally arranged diversion separator, the two ends of the diversion separator are respectively arranged at the two plates of the expansion box, the diversion separator is used for dividing the internal space of the expansion box into an upper space and a lower space, and the two sides of the diversion separator are respectively arranged at intervals corresponding to the box doorand a back plate of the expansion box; and the diversion separator is provided with a diversion fan with an air direction upwards, one side plate of the expansion box is provided with an exhaust fanwith an air direction outwards corresponding to the position of the lower space. The substation GIS current transformer secondary flooding box is suitable for a substation GIS device.