The invention relates to a method and a device for removing sulfur and carbon oxides from power plant flue gas in a combination mode, which are used for removing the sulfur and carbon oxides from the power plant flue gas at high efficiency and low consumption. The method comprises the following steps of: introducing high temperature flue gas subjected to electrostatic precipitation into a heat exchanger and heating decarburized solution in a removing process by using waste heat of the flue gas; feeding the heated decarburized solution into an absorption tower, decomposing ammonia water out and feeding the ammonia water back to an ammonia water storage tank; and allowing low temperature flue gas subjected to heat exchange to enter the removing process in combination with desulfuration and decarburization processes. The invention also provides the device for implementing the method. In the invention, the ammonia water is used as an absorbent, ammonia can be chemically circulated, and the cost of the absorbent is reduced; and the waste heat of the flue gas is effectively utilized to heat the decarburized solution, energy of a power plant can be utilized in a stepped way, and energy consumption during carbon capture is greatly reduced. The method and the device have the characteristics of high efficiency, high cleanness, low energy consumption, high integration of a desulfuration system and a decarburization system and have a wide application prospect on desulfuration and decarburization of a coal fired power plant.