The FAB-SAW test with different filling materials and big gap is carried out on two kinds of DH36 ship steel plates with same composition and different thicknesses,and the mechanical properties and microstructure characteristics of welded joints are analyzed. The results show that adopting FAB-SAW as backing welding and SAW for filling and covering, the tensile strength,bending property,hardness value, impact toughness and other properties of welded joints can meet the standard requirements; The weakest impact toughness of the entire joint is at the center of the weld, and the multi-layer and multi-pass welding is adopted for the surface weld center,so the impact value of the surface weld center is higher than that of the welding root. The broken welding wire and iron powder compositions of filling materials are different,but they have little effect on the impact value of root weld center. The base metal is manufactured by TMCP technology and designed with low carbon content,so the coarsening of the microstructure of the heat affected zone is not obvious and the impact toughness is good.