The invention provides a condensation treatment device of a boiler, and belongs to the technical field of boilers. According to the condensation treatment device, the problem that a water drainage opening of a condensation water box of a condensation treatment device of a conventional boiler is easy to block and inconvenient to clean is solved. The condensation treatment device of the boiler comprises an air inlet wind channel, a condensation heat exchanger, a condensation water box and a chimney, wherein an air outlet which is opened upwards is formed in the top of the condensation water box, and the chimney is connected to the air outlet; a water drainage opening is formed in the bottom of the condensation water box, a floor drain is arranged on the water drainage opening, and a water drainage pipe which is used for draining condensation water downwards is connected to the water drainage opening; the bottom surface of an inner cavity of the condensation water box is lower than that of an inner cavity of the condensation heat exchanger; an operating opening allowing to remove ash is formed in the side wall of the lower part of the condensation water box; and a water level detector is arranged in the condensation water box, a warner is connected to the water level detector, and the water level detector is positioned under the operating opening. According to the condensation treatment device disclosed by the invention, the operating opening is formed, so that ash removal is conveniently performed on the condensation water box, and the normal running of the condensation treatment device is guaranteed.