Abstract: Microstructures of base metal and brazed joints were analyzed using metallographic microscope, SEM and microhardness instrument, and the changing rule of strength of brazed joints was studied by testing microhardness of brazed joints and chemical com-position of fracture micro-section. The results show that shape of reinforcing phase of base metal are changed from particle to strip after brazing;there are few defects such as gas pores, slag inclusions, cracks and so on in brazed joints with N₂ atmosphere, which im-proves mechanical properties of brazed joints effectively, however there are many defects in brazed joints without N₂ atmosphere, which reduces mechanical properties of brazed joints seriously.