Disclosed is a plasma welding apparatus for a guide thimble and guide thimble end plug of a nuclear fuel assembly, which includes: a welding chamber (100) includes an end-plug inserting part (110) into which the end plug (10) is inserted, a guide-thimble inserting part (120) which is provided on the same axis as the end-plug inserting part (110) and into which the guide thimble (20) is inserted and fixed, a torch assembling part (130) to which a plasma welding torch (131) is assembled so as to make a right angle with the end-plug inserting part (110) and the guide-thimble inserting part (120), and argon inflow and outflow ports (141, 142) through which argon is supplied or discharged; an end-plug transfer unit (210) supplying the end plug (10) to the end-plug inserting part (110); and an guide-thimble transfer unit (220) transferring the guide thimble (20) to the guide-thimble inserting part (120).