The utility model relates to a back-door locking device for a 10 kV switch cabinet, in particular to a back-door locking device of a five-prevention locking system in a 10 kV metal armored central-positioned switch cabinet for high voltage distribution in power industry, and the back-door locking device belongs to the field of high-voltage switch cabinet. The back-door locking device is characterized in that: the device has reliable locking, easy installation, and no need for debugging; and a locking method of the device is that a back door is prevented from being opened by the back-door locking device when a grounding switch (1) is separated, and the grounding switch (1) is prevented from being separated when the back door is opened. The device comprises a back-door locking top block (5), a steering braking block (6), a back-door locking fixing plate (3), a back door locking bracket (9), a back door locking small shaft (4), and the like. The back-door locking device for the 10 kV switch cabinet solves the defects existing in the prior art that the assembly efficiency is low, the torque of an operating rod is large, the operation is laborious, a back-door locking device is not easy to adjust, and the like; and the back-door locking device has the advantages of convenient installation and debugging, reliable locking, smooth operation, and the like.