The invention discloses a narrow gap and deep groove welding head. The welding head comprises a hollow tabular welding head shell main body which is thin and long and is suitable for stretching into a narrow and deep groove gap for welding; the welding head is further provided with double gas protection systems, wherein the position of a secondary gas protection system is adjustable so that the surface of a melting pool can be fully protected and the welding quality is ensured; a protected gas lens is connected outside the air outlets of the double gas protection systems so that protected gas can be stably and evenly sprayed out, the surface of the melting pool is fully protected, and the welding quality is increased; a compulsory water cooling system is arranged, then a tungsten electrode fixing device is compulsorily water-cooled, and cooling water circularly flows so that a tungsten electrode can be fully cooled.