Abstract: Self-shielded flux cored wire for 9%Ni steel with Fe-Ni-Mn-Si alloy system was developed. This wire was welded by FCAW with no shielding gas. QLT heat treatment was carried out after welding. Mechanical properties, microstructure, and fracture morphology of welded joint were studied by tensile testing, low temperature impact testing,metallurgical analysis, and SEM. The results show that, The tensile strength of welded joint is 709 MPa,the yield strength is 580 MPa, elongation ratio is 26%, section shrinkage rate is 47%. The mechanical properties meet the requirement of the use of 9%Ni steel. The microstructure of the weld metal consists of fine grain ferrite and acicular ferrite. QLT heat treatment increased low temperature impact energy of weld metal from 48 J/cm² to 100 J/cm². It can significantly improve the low temperature toughness of the weld.