Abstract: By using spectrum analyzer,optical microscope and SEM,chemical composition and microhardness of tube material were tested,and metallurgical structure and fracture pattern of the joint were observed. It is found that there was widmanstaten structure in the joint and inclusion aggregated. And part area of the joint lacked of fusion. The analysis showed that overside of parameter in furnace tube joint welding,and unsuitable choices of the welding material were the main reason of the joint failure.