A process for simultaneously desulfurizing and denitrating the flue gas with seawater includes the following steps: 1) catalytically scrubbing the flue gas containing SO2 and NOx with the seawater to obtain purified flue gas and acidic seawater, optionally adding a certain quantity of iron ions into the seawater or applying magnetic field during scrubbing; 2) adding seawater into the acidic seawater while blowing air in so as to restore the quality of the acidic seawater up to the environmental standards. Also a device used in the process is provided.