The invention discloses a device and a method for treating calcined waste gas. The device comprises a zirconium rotary kiln, a cyclone dust collector, a Venturi scrubber and an electrostatic dust collector, wherein the zirconium rotary kiln is communicated with the cyclone dust collector through a gas inlet pipe; the bottom of the cyclone dust collector is communicated with the zirconium rotary kiln through a recycling pipe; the cyclone dust collector is connected with the Venturi scrubber through an exhaust pipe; the Venturi scrubber is connected with a clarifier through a first pipeline; theclarifier is connected with an overflow groove through an overflow pipe; the overflow groove is connected with the Venturi scrubber through a circulating pump; the Venturi scrubber is connected withan alkali washing tower through a second pipeline; the alkali washing tower is connected with the electrostatic dust collector through a third pipeline; and the electrostatic dust collector is connected with a chimney through an exhaust pipe. The device is novel in structural design, can effectively treat the waste gas produced in a process of producing zirconium oxide by basic zirconium sulfate and then discharge the waste gas after the waste gas meets the standard, and is high in environmental friendliness.