The invention relates to a multifunctional reaction tank for flue gas desulfurization and denitration, which belongs to the technical field of environment protection. The multifunctional reaction tank for flue gas desulfurization and denitration comprises a tank body (1), wherein at least one partition board (3-1) is arranged in the tank body (1) in the vertical direction for forming a structure of more than two oxidation inner cavities in one tank body, in addition, two adjacent oxidation cavities are mutually communicated, the upper part of each oxidation inner cavity is respectively provided with self-air-suction injection type air liquid mixers (7-1, 7-2, 7-3 and so on), the lower part of each oxidation inner cavity is respectively provided with oxidation liquid extraction outlets (12, 14, 16 and so on), and the lower part of the penultimate oxidation inner cavity is provided with a desulfurization liquid extraction outlet (13). The multifunctional reaction tank of the invention integrates the desulfurization liquid oxidation, the preparation and the storage into a whole body, and has a compact structure and overlapped functions, so the flow process of a desulfurization and denitration device is shortened, the energy consumption is reduced, and the investment is saved. The absorbing liquid ingredient proportion of the traditional desulfurization and denitration process is changed, the formation of aerosol is reduced, and the desulfurization efficiency is improved.