Abstract: In order to shorten the replacement time of thimble tube and reduce the time of nuclear power overhaul work,the thimble tube can be temporarily blocked by welding blocking process when the thimble tube is worn out,and then uniformly replaced when the number of blocked thimble tube does not meet the demand of neutron measurement in the core of the reactor.According to the material and structural characteristics of the thimble tube and the difficulties of manual welding repair,the automatic welding process of thimble tube plugging is developed to improve the quality of thimble tube plugging welding repair and to protect the welding staff from environmental dose.By adjusting the welding base value and peak current,welding voltage and shielding gas flow,the welding process parameters and welding specimens with no surface defects and residual height meeting the requirements are finally obtained.The test results indicate that the welding current varies between 60 and 66A,which means that the casing and plug can realize good fusion and connection,and can obtain a weld seam with no defects on the surface and a residual height of≤0.1mm,and the weld seam morphology conforms to the RCC-M standard.The development of the welding process parameters has guiding significance for nuclear power field welding construction.