The invention discloses a catalyst for simultaneous flue gas desulfurization and denitration and a preparation method thereof. The catalyst comprises a composite support, a cocatalyst and an active component supported on the composite support. The catalyst comprises the following components by mass: the composite support 50%-70%, the cocatalyst 5%-15% and the active component 15%-45%. The composite support is composed of zirconia, alumina and activated carbon. The composite support comprises the following components by mass: the zirconia 40%-60%, the alumina 10%-20% and the activated carbon 20%-50%. The cocatalyst is selected from one or more of Na2O, NiO and ZnO. The active component is one or more of Fe2O3, Na2O, transition metal Mn or vanadium pentoxide. The catalyst has high activity and stable performance, can be repeatedly used, does not cause secondary pollution, and is more beneficial to reduce the amount of carbide slag under the unit removal amount, low in cost, good in stability and high in catalytic activity.