The invention provides a cavity. A spraying piece is arranged in the cavity; a spraying hole penetrating through the spraying piece is formed in the spraying piece; the spraying piece comprises a first spraying piece and a second spraying piece; multiple first through holes are formed in the first spraying piece; multiple second through holes are formed in the second spraying piece; and the first spraying piece and the second spraying piece are vertically overlapped to communicate the first through holes with the second through holes to form the spraying hole. Compared with the prior art, the cavity can more convenient to machine the first spraying piece and the second spraying piece, so that the machining complexity is prominently simplified. Meanwhile, the area and the aperture of the spraying hole can be adjusted through adjusting the relative positions of the first spraying piece and the second spraying piece, so that more process demands can be conveniently realized.