The invention discloses a device and a method for treating and using fume waste heat during harmful tail gas treatment. The device comprises a heat-exchange pipe arranged in a fume transportation pipeline which is communicated with a tail gas absorption tower, wherein an ammonium sulfate solution which is converted by the absorption tower in multiple steps and then is stored in a storing tank is led in the heat-exchange pipe; an outlet end of the heat-exchange pipe is communicated with a hot material liquid pond close to the heat-exchange pipe; an upper end outlet of the hot material liquid pond is communicated with the tail gas absorption tower through a pipeline and a corrosion-resistant vacuum pump; a lower end outlet of the hot material liquid pond is communicated with a liquid inlet of the storing tank through a pipeline and a corrosion-resistant infusion pump; a liquid outlet of the storing tank is communicated with an inlet end of the heat-exchange pipe; the flowing direction of the ammonium sulfate solution in the heat-exchange pipe is reverse to the flowing direction of fume in the fume transportation pipeline. Fume waste heat is effectively treated and used by a heat-exchange method, secondary pollution is basically avoided, the cost is reduced, the waste is changed into useful substances, equipment is simple in structure, relatively low in manufacturing cost, convenient to operate and easy in grasp of operation technology.