The welding at the junction of the base layer and cladding layer of the stainless steel clad plate belongs to dissimilar steel welding. Its weldability is affected by various factors such as the physical properties, chemical properties, joint form and filler metal of the cladding layer and base layer, and often causes welding cracks and other problems. Through the analysis of the welding quality of the longitudinal seam of the cylinder body, the cylinder section and the circumferential seam between the cylinder section and the head in the pressure vessel, the reasons for the low qualified rate of welding of stainless steel clad plates in specific projects are explored. The specific improvement measures are proposed, such as the use of combined grooves design and changing the welding sequence. Through the implementation of improvement measures, the welding qualification rate of the pressure vessel Q345R/S31603 stainless steel clad plates in this project has been increased from 78% to 100%.