The utility model relates to a flue gas carbon dioxide gathering pretreatment device. The flue gas carbon dioxide gathering pretreatment device comprises a water washing tower, a water washing liquor pump, a water cooling tower, a settling pond, a channel online pH meter, a gas-liquid cyclone separator and an alkaline liquor storage tank, and is characterized in that the water washing tower, the water cooling tower, the cyclone separator and the settling pond are vertically mounted at certain intervals; flue gas enters the water washing tower for water washing through an electromagnetic switch valve at the lower part of the water washing tower and then enters the cyclone separator for separation from the upper top part, clean flue gas after separation enters a next process of gathering carbon dioxide gas from the top of the cyclone separator, and separated water and purities enter the settling pond for settling through an electromagnetic switch valve at the lower part of the cyclone separator; the impurities and water filtered by the water washing tower enter the upper part of the water cooling tower for cooling through control of the electromagnetic switch valve at the lower part of the water washing tower and pressurization of a water pump, the cooled impurities and water enter the settling pond from the bottom of the water cooling tower, and water settled through the settling pond is pumped by a circulating water pump into the upper top part of the water washing tower for flue gas recirculation water washing; alkaline liquor inside the alkaline liquor storage tank is controlled by the electromagnetic switch valves and the electromagnetic switch valves are controlled by the channel online pH meter to increase/reduce alkaline liquor to/from the settling pond, and the pH value of the settling water is controlled in a range of 7-7.5.