The invention provides an SCR (selective catalytic reduction) device provided with a single reactor. In the prior art, larger space is required for arranging double reactors, more steel structures and reactor protective boards are used, and for part of reconstruction projects, the arranged double reactors cannot meet original steel structure and foundation requirements; and further, uniformity of flow fields in reactor inlets of the arranged double reactors is poorer, and more guide plates are required. The SCR device provided with the single reactor comprises two economizer outlet flues (1) which are connected with a reactor inlet flue (2) respectively, and the reactor inlet flue (2) is connected with an SCR device single reactor (3) which is mounted on a reactor support beam (4) and connected with an air preheater. The SCR device provided with the single reactor is applied to an SCR reactor of a boiler.