Abstract: The special TIG welder was used to weld the Canopy weld of the control rod drive mechanism of nuclear power plant.The machined Y-ring was selected as the filling material for the to study the microstructure and properties of machined Y-ring welds.The results show that the Y-ring Canopy weld is machined by TIG welding and has good shape,moderate width and good metallurgical fusion with the base metal.The weld structure is mainly composed of plate or skeleton ferrite and fast solidifying columnar austenite.After 23.1MPa to 23.3MPa water pressure test,the surface of the Canopy weld has no leakage,no visible deformation.On the surface of the results,the weld hardness is about 210HV,and the weld hardness distribution is uniform.The research provides valuable experience for machining Y-ring for the lower Canopy welded joint of control rod drive mechanism in nuclear power plant.