The invention relates to a novel narrow-gap gas metal arc welding gun, a guide mechanism is arranged on the lower end of a rod assembly, and is inclined relative to the central axis of the rod assembly, and the end of the guide mechanism is provided with a tip. The invention effectively solves the problem of narrow-gap welding that sidewall fusion is defective, and also solves the problems of welding gun cooling and accidental sidewall arcing, and the novel narrow-gap gas metal arc welding gun is flexible and convenient to use, and has the advantages of stability, reliability, higher welding efficiency, better welding quality and more stable welding process. The novel narrow-gap gas metal arc welding gun is suitable for all the fields which have high requirement on welding efficiency, welding quality and welding economy and can use the narrow-gap welding technology, and is applicable to the arc welding of metal materials in the industries of electric power, ships, buildings, transportation and the like, and the advantage is more obvious for the narrow-gap welding of thick-walled members, particularly when the requirement on welding quality and welding efficiency is high.