The invention discloses an internal wedge-shaped piece bolt and a prestress adjusting method thereof, and relates to the technical field of bolt thread pre-tightening force. Comprising a bolt body, external threads are arranged on the outer wall of the bolt body, a nut is connected outside the bolt body, a wedge-shaped hole extending inwards is formed in the end face of the end, provided with the external threads, of the bolt body, and a threaded hole is formed in the bottom end of the wedge-shaped hole; a through hole is formed in the wedge-shaped piece in the axial direction of the wedge-shaped piece; the end, provided with the threads, of the pressure bolt penetrates through the through hole and is in threaded connection with the threaded hole, and along with increase of the thread screwing length of the pressure bolt and the threaded hole, a bolt head of the pressure bolt extrudes the wedge-shaped piece to move into the wedge-shaped hole, so that the position, provided with the external threads, of the bolt body and the nut are tensioned. According to the bolt with the internal wedge-shaped part, the bolt head of the pressure bolt continuously extrudes the wedge-shaped part, so that the wedge-shaped part extrudes the bolt body, the tightness and safety of connection are improved, and dangerous accidents caused by looseness of the bolt are avoided.