Abstract: Narrow gap laser welding is an advanced welding technique with considerable advantages such as large welding thickness, strong flexibility and minimal deformation after welding, which has been widely investigated in the context of thick plate structures. In this paper, historical development of narrow gap laser welding was comprehensively reviewed and welding process of narrow gap laser welding was briefly summarized. Then, factors affecting welding quality were deeply expounded and common welding defects of narrow gap laser welding were discussed. Furthermore, a control strategy for optimizing welding quality was summarized, which was categorized into beam modulation, external physical fields and other methods. Laser oscillation is widely used in narrow gap laser welding, electromagnetic and ultrasonic assistance will also improve weld quality, and hot wire welding can improve welding efficiency. Moreover, application of computer-aided approaches to narrow gap laser welding was explored in this paper. Finally, future development of narrow gap laser welding was prospected.