The invention relates to a cyclic crystallization Fenton fluidized bed and a method of using the same to treat difficult-to-treat wastewater and belongs to the technical field of wastewater treatment. The cyclic crystallization Fenton fluidized bed comprises a mixing area, a reaction area, a fluidizing area, a precipitation area and a water outgoing area. The method includes steps that wastewater and an agent are enabled to enter the mixing area through a pump for mixing, a reflux pump enables mixed liquid to circulate from the top to the bottom of a reactor, a filler in the fluidizing area under impact of the mixed liquid at the bottom starts fluidizing, iron in a solution crystallizes on the surface of the filler, and the wastewater then enters the precipitation area to remove part of floc and is finally discharged through a water outlet.. By the method, pollutants in water can be removed effectively, total iron content of outgoing water is reduced, and the method has good treatment effect on various kinds of difficult-to-treat wastewater.