The invention provides a special positioning and clamping device for an automatic submerged pipe flange connecting machine. The device comprises a master jaw 1, a hinged hydraulic cylinder 2, a jaw 5, a hydraulic cylinder mounting lug 6 and a jaw mounting lug 8, wherein the hydraulic mounting lug 6 is fixed on the master jaw 1; the hinged hydraulic cylinder 2 is connected with the master jaw 1 through the hydraulic mounting lug 6 and is connected with the jaw 5 through a pin shaft 3; the jaw 5 is connected with the master jaw 1 through a rotating shaft 4; and the jaw mount lug 8 has two pieces which are welded at two sides of the master jaw respectively. The invention provides a positioning and clamping device for a deepwater automatic flange connecting machine which can adapt to deep-sea environment and meet the operational requirements of the deepwater automatic flange connecting machine on positioning and clamping.