The utility model discloses a coke dry quenching furnace water seal tank water supplementing device and relates to the technical field of manufacturing of coke dry quenching equipment in coking plants. The device comprises a water tank and a water seal tank, wherein a water inlet pipeline is divided into two paths, one path is communicated with the top of the water tank through a water inlet valve, and the other path is communicated with the water seal tank through a valve in a maintenance bypass pipeline; an overflow pipe is arranged at the upper end of the water tank and is communicated with the maintenance bypass pipeline through a conical hopper and a normal water supplementing valve; an emergency pipeline is arranged at the lower end of the water tank and is communicated with the water seal tank through an emergency water supplementing valve; and the emergency water supplementing valve is in a normal open state on the emergency pipeline. By the device disclosed by the utility model, the problems that the water seal tank is subjected to dry heating, even fractures due to water pressure fluctuation, water break or failure during coke dry quenching production can be solved.