The invention is a two-stage desulfurizing and dust-cleaning device, including a shell and a lye circulating system, and its character lies in that it is composed of low-resistance spray head, low-speed venturi tube, impact baffle and annular-arranged baffling plate demister, which are installed in turn from top to bottom. Its beneficial effect: during two-stage desulfurization circulation, adopting a low-speed venturi tube plus impact baffle structure to make the gas resistance low and desulfurizing efficiency high and play a role in primary dehydrating, and the low-resistance demister on the top of the desulfurizing tower can thoroughly eliminate fine water drops in the fume, ensuring that the fume carries no water. It is of a unit structure, convenient for installing and overhauling, the baffling plate can thoroughly dehydrate all the more because of vertical installation, avoiding secondary carrying of the fume, and it has higher flow speed and compacter device, saving the space.