The pressurizer immersion heater,as one of the important components of the pressurizer in PWR nuclear power plant,is directly immersed in the coolant with the high temperature, high pressure and high nuclear radiation in the primary circuit. As the pressure boundary to bear the external pressure of the primary circuit,the quality of the weld between the sheath and end plug is required very strictly and the structure is very special. By studying the weld structure and welding technology,a kind of welding procedure which not only meets the requirement of high quality,but also can be applied in engineering is given.