Abstract: 9Ni steel was welded with submerged arc welding process,and the microstructure and fracture appearance of welded joints were analyzed. The effect of heat input on the microstructure and low temperature impact resistance of the joints was studied. The results show that with the increase of the heat input,dendritic segregation and precipitation phase in the weld reduce,and fracture dimples become larger and deeper,which make the impact resistance of the joints increase. The joints in different input can meet application requirements,which impact absorbing energy is superior to standard at -196℃ and hardness is inferior to 400 HV. The experiment results can be used as theoretic basis for making welding procedure of 9Ni steel.