The invention belongs to the technical field of seawater desulfurization and in particular discloses a device for desulfurization and dedusting of smoke of a ship through seawater. The device comprises an outer casing, a gas inlet pipe, an exhaust pipe, a water inlet pipe and a drainage pipe, wherein both the gas inlet pipe and the exhaust pipe are inserted into the top end of the outer casing; the water inlet pipe is inserted into the upper side of the left side wall of the outer casing; and the drainage pipe is connected with the bottom of the outer casing. Seawater is added into the outer casing through the water inlet pipe, the seawater is discharged out from the drainage pipe, through the function of sufficient contact of the seawater with a flue gas, impurities in the flue gas can beadsorbed, meanwhile, a desulfurization function is taken into play, sufficient contact is achieved, and the desulfurization effect is good; through a floating dust filtering mechanism, impurities andfoams generated by the flue gas desulfurization can be filtered and are prevented from floating up, and thus a primary filtering effect is achieved; and when the seawater is discharged through an overflow pipe or the drainage pipe, impurities in the seawater can be filtered through a discharge filter device.