Abstract: 9Ni steel plates were welded by manual arc welding and automatic submerged arc welding, respectively, and microstructure and mechanical properties of two kinds of welded joints were studied by tension, bending and impact testing, as well as microstructure and fracture observing. Results show that the microstructure of weld metal in the two welded joint all consistsed of austenitic, and that of heat affected zone all consistsed of martensitic. Crystal morphology of weld metal of manual arc welded joint was dendritic crystal, segregation degree was relatively large and martensitic in heat affected zone was bulky. Crystal morphology of weld metal of automatic submerged arc welded joint was cellular dendrites, segregation degree was relatively low, lath martensitic in heat affected zone was thin and martensite lath bundle was relatively more. For the two welded joint, tensile properties and blending properties were well, and impact toughness of the automatic submerged arc welded joint at low temperature was better than that of the manual arc welded joint. The dumples on impact fracture of automatic submerged arc welded joint were bigger and deeper, and they distributed evenly.