Abstract: High strength low alloy steel SA738GR. B was applied to steel containment vessel in the third generation of nuclear power AP1000 for the first time,and automatic welding process was tested by special welding wire ER90S-G for SA738GR. B steel plate,then the product simulation experiments were carried out. The results show that the impact properties of the welded joint can satisfy the technology requirements of the containment vessel within the range of heat input 12 ～ 29 kJ/cm. In the above heat input range,automatic welding procedure qualification were tested on 1G/2G/3G welding position as well as the various mechanical properties can satisfy the requirements of technology. In addition,under the precondition of the optimal process,the optimal parameters of automatic welding process were determined and applied to the simulation product and the various mechanical properties can satisfy the requirements of technology.