The invention discloses a selective catalytic reduction device by directly spraying a urea solution and a method thereof, and relates to the technical field of environmental protection. The device comprises a plurality of groups of spray guns for spraying the urea solution, which are arranged at an inlet flue before a selective catalytic reduction (SCR) reactor, and a mixer and a catalyst which are arranged along the flowing direction of flue gas in turn, wherein each spray gun is connected with a urea solution tank through a metering distributor. Compared with the prior art, the invention has the advantages that: the urea solution is directly sprayed into the flue to thermally decompose the supplied ammonia, the operating cost and equipment investment are reduced, the space is saved, and the device is safe and reliable to use.