At present,the domestic mainstream nuclear power reactor type is the second-generation pressurized water reactor type. The nozzle and safety end of the key equipment are welded with different types of steel welded joints. The joint type is: the surfacing of stainless steel isolation layer（ER309L+ER308L） is conducted at the nozzle end, and then the butt welding of stainless steel welding consumables（ER308L） and stainless steel safety end is conducted. The metallurgical structure,impact properties,micro Vickers hardness distribution,micro-curve energy spectrum and fracture morphology of 16MND5/309L side bond line of 16 MND5/309L/308L/Z2CND18-12N dissimilar steel welded joints made by domestic second generation nuclear power technology are analyzed. The results show that the impact performance of the 16MND5/309L side bond line is generally low,and there are brittle fractures in some areas. The brittle fracture is generally located in the martensite zone near the bond line,mainly along the crystal fracture,and the overall distribution of the martensite zone is not uniform,and the width range has no obvious rule. The hardness value of the 16MND5/309L side bond line is the highest,and the hardness value reduces towards both sides of the 16MND5/309L interface,and a significant hardness reduction area appears near the bond line（about 0.5～1 mm） on the 16MND5 side. The carbon migration and brittle transition layer（martensite zone） at the interface of 16 MND5/309L are obvious,and a recarburization layer and a decarburization layer are formed on both sides of the bond line,resulting in a serious decline in the impact toughness of the 16MND5/309L side bond line.