A changeable positioning device for dental drilling comprises a base, a guide body and a positioning block. The base comprises a top end, a bottom end, a first outer wall, a first inner wall, a first guide groove, at least one first recess and at least one second recess. The at least one protrusion can be slidably fitted with the at least one first recess and the at least one second recess, thereby the second guide groove of the guide body will not be synchronously moved with a drill during drilling toward the axial direction of the guide body. The distance between the two extension portions is smaller than the diameter of the second inner wall at the same plane that is perpendicular to the axis of the guide body so that the drill will not deviate from the guide groove, thereby increasing the stability and precision of drilling.