The invention discloses a slag flushing water filter of a blast furnace. The slag flushing water filter comprises a shell, a filtering disc, a transmission device, a rotary seal, a rotary support, a bracket, a water inlet and a water outlet, wherein the water inlet and the water outlet are respectively formed in the lower part and the upper part of the shell, the transmission device is distributed at the upper part of the shell, the filtering disc, the rotary support and the bracket are arranged inside the shell, the upper part of the filtering disc is connected with the transmission device, the lower part of the filtering disc is connected with the rotary support, the bracket is fixed between the rotary support and the shell, a filtering net covers the top of the filtering disc, the rotary seal is distributed between the filtering disc and the shell; slag flushing water is filtered by the filtering net at the top of the filtering disc, slag is remained in the filtering disc; after the filter works for a long time, water enters the shell of the filter from the water outlet in the upper part of the filter, the slag is discharged from the water inlet in the lower part of the filter by means of a flushing action. The slag flushing water filter of the blast furnace, disclosed by the invention, has an efficient filtering and pollution-discharging function, is used for solving the problem of blockage of the slag flushing water of the blast furnace, and has an important significance in recycling secondary energy sources.