The invention discloses a device for fixing a protective arm casting pipe in a drill hole. The device comprises the protective arm casting pipe and a casing pipe support, wherein the casing pipe support comprises a casing pipe and a supporting structure, one end of the supporting structure is fixed to the outer wall of the casing pipe, the other end of the supporting structure is in a tree branch shape on the outer wall of the casing pipe, and one end of the casing pipe is arranged outside the protective arm casting pipe in a sleeving mode. Compared with the prior art, the device has the following advantages that the protective arm casting pipe in the drill hole is fixed at a designated position and does not slip off, the protective arm casting pipe can be only arranged in a coal seam, the protective arm casting pipe is not needed to be removed in the whole drilling process, and a protective arm casting pipe support manufacturing method is simple and can be widely applied to a hole protection structure of a coal mine drill hole.