The invention relates to a device and method for removing various pollutants in flue gas through photoassisted catalytic oxidization. Flue gas waste heat utilizing and atomizing generation device is arranged in a pipeline between an air pre-heater and an electrostatic dust remover and is of a structure that a small pipe is sleeved with a large pipe; the large pipe is used for conveying a composite oxidization agent; compressed air in the small pipe makes the composite oxidization agent in a boiling state; meanwhile, hot flue gas and the composite oxidization agent exchange heat so that the composite oxidization agent can be atomized into ultrafine liquid drops; the atomized composite oxidization agent enters a photoassisted catalysis and activation reaction device to be catalyzed and activated, various free radicals are generated and ejected out of an outlet of the photoassisted catalysis and activation reaction device and make contact with flue gas with dust removed, NO in the flue gas is converted into high-valence-state NOx, HgO is oxidized into Hg2+, NOx, Hg2+ and SO2 enter an absorbing device along with the flue gas and are absorbed and removed, efficient and synergistic desulfurization, denitration and mercury removal are achieved, removed products are high-quality compound fertilizer, resource utilization is facilitated, and high economic and environmental benefits are achieved.