Disclosed is a mouthpiece assembly, including a lower mouthpiece cover and an upper mouthpiece cover. The lower mouthpiece cover is provided with a first air inlet passage and a first air outlet passage. The upper mouthpiece cover is provided with an air exiting hole. The upper mouthpiece cover can move relative to the lower mouthpiece cover. When the upper mouthpiece cover is in a first connection state relative to the lower mouthpiece cover, the first air inlet passage is in communication with the outside, and the first air outlet passage is in communication with the air exiting hole; and when the upper mouthpiece cover is in a second connection state relative to the lower mouthpiece cover, the first air inlet passage and the first air outlet passage are closed by the upper mouthpiece cover.