Abstract: The pulsed ultra-narrow-gap welding (UNGW) was applied to 1Cr18Ni9Ti austenitic stainless steel plate with 20 mm thickness. The microstructure, mechanical properties and corrosion resistance of the pulsed UNGW joint were analyzed. The results show that the microstructures of backing weld zone in pulsed UNGW joint were austenitic equiaxed grain+lath δ-ferrite; the microstructures of filling bead and cover pass weld zone were columnar austenite+lath and cellular δ-ferrite. The microstructures of partially melted zone were austenite + vermicular δ-ferrite; the microstructures of imperfect mixing zone were austenite+δ-ferrite, and their shape was disorderly. The microstructures of heat affected zone were austenite+striped δ-ferrite. The ductility and toughness of the pulsed UNGW joint were better than those of the direct-current UNGW joint, but the strength was lower than that of the direct-current UNGW joint. The corrosion resistance of fusion zone+heat affected zone, weld zone, whole joint and base metal of the pulsed UNGW joint increased in turn in NaCl solution. The intergranular corrosion resistance of the pulsed UNGW joint in nitric acid solution was worse than that of the base metal without sensitizing and the direct-current UNGW joint, but was better than that of the sensitized base metal.