The invention provides an emission reduction device for a generator set so as to reduce poisonous gas discharged by the generator set in real time. The emission reduction device comprises the generator set, wherein the generator set is provided with an exhaust pipe, one end of the exhaust pipe is provided with a silencer, a rotating shaft of the generator set is sleeved with an air inlet device, the air inlet device comprises an air inlet cover, an air inlet rotating wheel and an air inlet bottom shell, three or more blades are arranged on the air inlet rotating wheel in the circumferential direction, an air inlet and an air outlet are formed in the air inlet bottom shell, the air outlet is connected with an air supplementing pipe, and the tail end of the air supplementing pipe is connected with an exhaust pipe. In use, due to the fact that the air inlet device is connected to a crankshaft in a sleeving mode, the air supplementing amount of the air inlet device corresponds to the rotating speed of the crankshaft, the fresh air with the corresponding amount can be supplemented and fed in real time according to the exhaust gas emission amount of an engine, and the poisonous gas discharged by the generator set can be reduced in real time.