The thermocouple plugs used in spacecraft thermal test are manually welded. With the increase of model development tasks in China,the problems of low efficiency of manual welding process and insufficient welding quality have been exposed. In order to ensure the production progress,improve the efficiency of plug welding and the quality of welding joints,a welding robot is introduced to realize the automatic welding process of thermocouple plugs. In order to solve the problem that different batches of copper wire butt welding and thermocouple have more than one welding joint under automatic welding process,the comparative tests of tension resistance test,temperature measurement performance test under normal working conditions and temperature measurement performance test under extreme tension deviation are carried out by using comparative method. The reliability of automatic welding process for thermocouple plug is verified through comparative analysis of test data.