The invention discloses a device for measuring the flowing speed of desulfurized flue gas, and a measurement method of the device. The device comprises a speed measurement part which is laid on a fluecorridor and is vertically disposed in the flowing direction of the desulfurized flue gas; a plurality of speed measurement assemblies which are disposed at the speed measurement part; at least two speed measurement units which are disposed on a speed measurement skeleton, wherein the speed measurement units are uniformly distributed in the speed measurement part; a dynamic pressure end which isdisposed at one side, facing an incoming wind direction, of the speed measurement units; and a static pressure end which is disposed at one side, backing on to the incoming wind direction, of the speed measurement units. The device is resistant to corrosion, is accurate in measurement, is high in precision, achieves the real-time response, is stable in performance, and is good in adjustability. The precision of a flow speed coefficient is high, and the stability is good. Meanwhile, the device has a self-deashing function.