The invention relates to a companion flange protective device and a protective method. During the packaging and transportation processes of conventional companion flanges, the flange shape is irregular, so that during the boxing process, the flanges are placed through universally adopting the method that the sealing surfaces are placed downwards; while as rubber blankets or wood boards for separating the flanges are liable to move, the risk that each flange and the adjacent flanges are damaged due to collision during the hoisting and transportation processes cannot be completely avoided; only one layer of flanges can be placed in one wooden box to protect end grooves and surfaces of the flanges, and if the number of the companion flanges required by a device is relatively large, a plurality of wooded boxes are needed for packaging the companion flanges. The companion flange protective device comprises an annular plate (1), wherein a gasket (2) is arranged between the annular plate and the companion flange; a cylinder (3) is arranged on the annular plate; a cover plate (4) is arranged at the top end of the cylinder; the annular plate and the cylinder are connected in a welding manner; and the cylinder and the cover plate are connected in a welding manner. The companion flange protective device and the protective method are applied to stable fixing and packaging of the companion flanges.