The invention discloses a single-tower oxidizing desulfurization and denitration device and a single-tower oxidizing desulfurization and denitration method. The device comprises a cylindrical absorption tower body, a gas inlet cylinder positioned at the lower part of the absorption tower body, a gas exhaust cylinder positioned at the upper part of the absorption tower body, an absorbent pool and absorption systems arranged in the absorption tower body, and a tower exterior buffer tank connected with the absorption tower body. The single-tower oxidizing desulfurization and denitration device is sequentially divided into the absorbent pool, the lower absorption system, an oxidizing system, a separating system and the upper absorption system from bottom to top along flue gas flow. Flue gas enters the absorption tower body from the gas inlet cylinder, and sequentially passes through a stirrer, a lower spraying layer and a lower demister, wherein a desulfurization agent is sprayed in the lower spraying layer to absorb SO2 therein, the flue gas from which the SO2 is removed enters the oxidizing system. A process and the system are simple, desulfurization and denitration functions can be efficiently realized, multiple operation modes can be suitable for multiple types of flue gas, sulfur nitrogen resources can be independently recycled, and the system and the method can be widely applied to desulfurization and denitration treatment on the flue gas or waste gas.