The utility model provides a drill bit that is used for drilling variable aperture stake hole, including the drill bit body, fixed surface is provided with a plurality of otic placodes outside the upper end of drill bit body, all is provided with down the connecting rod on every otic placode, and the one end of lower connecting rod is articulated with the otic placode, and the other end is articulated with ream bit, is provided with the reaming hobbing cutter on ream bit's the lower terminal surface, still be provided with the pneumatic cylinder on the drill bit body, the piston rod of pneumatic cylinder is articulated with the middle part of lower connecting rod, and the cylinder of pneumatic cylinder is articulated with the lower extreme surface of drill bit body, the lower fixed surface of drill bit body is provided with the hob head, is provided with flat hobbing cutter on the lower terminal surface of hob head. The utility model discloses can realize that the expansion bit becomes the needs of the arbitrary diameter reducing of width of cloth within range drilling, is applicable to the engineering stake hole of the little aperture in upper portion, lower part large aperture.