Abstract: The cracking of welded joints of dissimilar metals is the main cause of nuclear power accidents.It is urgent to develop new materials and new process to improve the weld quality.Traditional arc welding has some problems, such as low efficiency, large heat input and serious deformation.Heat input, filling and deformation of narrow gap arc welding are lower than those of traditional arc welding.Compared with narrow gap arc welding, narrow gap laser welding with filling wire addition has narrower groove, lower heat input, smaller deformation and higher precision.The previous research indicated that narrow gap laser welding with filler wire addition could meet the requirements of the nuclear pressure vessel manufacture.It was expected to become a new method of the dissimilar metal welding.However, there were still three main problems existing in the available narrow gap laser welding with normal laser and filler single wire addition process.Firstly, the interface was easy to produce incomplete fusion.Secondly, the viscosity of molten metal was high and the fluidity of molten pool was poor resulting in the uneven distribution of alloy elements.Thirdly, the eutectic phase with low melting point precipitated too much along the grain boundary, which couldn’t take into account the ability of weld to resist liquefaction crack, stress corrosion crack and high-temperature plastic crack.The applicant believed that the welding heat source and filler materials were the two key factors to solve the above problems.Highlights:(1)The development and trend of welding materials for nuclear dissimilar metals were systematically discussed.(2)The narrow gap laser welding had the potential to become a new method of welding dissimilar metals in a nuclear power.(3)The welding heat source and welding materials were the two key factors to solve problems such as incomplete fusion of interface, poor fluidity of molten pooland eutectic phase with low melting point precipitated too much along the grain boundary in narrow gap laser welding with filler wire addition.