The invention relates to a two-stage flue gas desulfurization tower and a ladder-level flow equalization and collection device thereof. The ladder-level flow equalization and collection device comprises a girder which is arranged along a radial direction of a flue gas desulfurization tower and is used for dividing the cross-section of the flue gas desulphurization tower into a number of fan-shapedregions, a plurality of small sub-beams are arranged in each one of the fan-shaped regions in parallel at intervals, the heights of the tops of the small sub-beams are decreased step by step from inside to outside, each two adjacent small sub-beams in the same region are connected through a liquid collection plate, the liquid collection plate is provided with sieve pores for gas flow equalizationand inclined spray holes, the liquid collection plate at the outermost side is provided with a liquid falling tank and the liquid falling tank is communicated with a return port on the wall of the desulphurization tower. The flow equalization and collection device has a small absorption tower height space so that the lift of a circulating pump in the second absorption stage is greatly reduced andthe two-stage flue gas desulfurization tower only needs one absorption tower slurry tank.