The invention relates to an OVD deposition cavity device for preparing an optical fiber preform. The device comprises an exhaust pipe, a first-stage buffer chamber, a second-stage buffer chamber and adeposition chamber, wherein the exhaust pipe, the first-stage buffer chamber, the second-stage buffer chamber and the deposition chamber are sequentially arranged from top to bottom, a wind inlet isformed in the bottom of the deposition chamber, a deposition core rod and a deposition blow lamp are arranged in the deposition chamber, the deposition chamber is in a house shape, the upper portion of the deposition chamber is trapezoidal, the lower portion of the deposition chamber is square, the top of the deposition chamber is in butt joint with the slit of the second-stage buffer chamber, thelower portion of the second-stage buffer chamber is inverted trapezoidal, the first-stage buffer chamber is in a circular tube shape, a wind supplementing pipe is arranged on the end surface of the first-stage buffer chamber, a wind supplementing valve is arranged on the wind supplementing pipe and used for adjusting the opening and closing size of the wind supplementing pipe, the first-stage buffer chamber is vertically communicated with the second-stage buffer chamber through a plurality of second-stage branch pipes distributed side by side in the axial direction, and the exhaust pipe is communicated with the first-stage buffer chamber through two arc-shaped pipes in a bilateral symmetry manner. According to the invention, the distribution uniformity of the gas flow in the deposition chamber along the axial direction of the deposition core rod is improved, the air pressure in the deposition chamber is stabilized, the wrapping area of the flame of the blow lamp on the deposition corerod is increased, and the collection rate of SiO2 powder is increased.