The utility model provides an external flue gas desulfurization tower filter, including box, import pipe, outlet pipe and built -in filter screen, the box is equipped with import pipe and outlet pipe respectively on relative two sides, and import pipe and outlet pipe all communicate the inside of box, built -in filter screen is in with the parallel setting of port face of import pipe the inside of box, and be two cavities with the internal partitioning of box, be connected with imported pipe valve door on the port that imported tub was kept away from the box, the utility model discloses a filter is installed between desulfurizing tower and desulfurization circulating pump import pipe pipeline, and cubic debris in the desulfurizing tower are blockked by built -in filter screen at the in -process that flows and are unlikely to to block up the desulfurizing tower and spray a layer nozzle, in addition, need clear up more for a long time in that cubic debris are long -pending more, can on -line cleaning as long as close filter import pipe valve door, and do not need to stop whole desulfurizing tower system, accomplish online maintenance, maintenance time can accomplish half a day, great maintenance time, the the cost is reduced of having shortened.