The invention relates to the machinery field and particularly relates to a generator unit. An air-cooling power low-noise unit with an independent air duct comprises a shell, wherein a fuel engine anda generator are arranged in the shell, a cover body is arranged outside the shell, an air flow channel is enclosed by the cover body and the shell, an air inlet and an air outlet are arranged in thecover body, and the air inlet and the air outlet are used as the air inlet end and the air outlet end of the air flow channel; one side of the cover body is provided with the air inlet end, and the opposite side is provided with the air outlet end; and the air inlet end is located below one side of the cover body, and the air outlet end is located below the other side of the cover body. By additionally arranging one air flow channel between the cover body and the shell, cooling can be carried out on the generator without affecting the power of the generator. Besides, the shell also can be prevented from being in direct contact with the cover body, so that temperature at the outer part of the cover body is prevented from being transferred to the shell.