This paper reviews the research of narrow-gap TIG welding. It contains narrow-gap welding with double arcs, narrow-gap welding with double wires, compounded narrow-gap welding, TIG welding under controlled magnetic arc and ultra-narrow-gap welding. It analyzes the merits and drawbacks of every manner in narrow-gap welding. Considering the little groove angle and small gap, how to make sure sidewall fusion, the improvement of fusion welding forming and the prevention of weld crack are focal points of narrow-gap welding researches. The further development of electrical and visual sensors can lower the precision of work piece assembling and solve the central location problem of electrode. Narrow-gap welding will have a good application foreground.