The invention relates to a method for treating a thermocouple conduit leakage in an in-core instrumentation system. The method comprises the following steps of cutting a second portion of the leakingthermocouple conduit, drilling a conduit seat to form a filling hole and forming a circular corner at the connecting joint between the side wall of the filling hole and the bottom of the filling hole,arranging a plug with a chamfer in the thermocouple conduit and sealing the thermocouple with the plug to make the circular corner and the chamfer form a groove, and carrying out welding and sealingon the groove. The above method effectively solves the problem of the leakage of the thermocouple conduit in the in-core instrumentation system. Besides, during the welding, the root of a welding seamis easily exposed to the viewing angle range of a welder, and a tungsten pole can overcome space obstacle to more easily reach the root of the welding seam so that the quality of the root of the welding seam is greatly improved. The invention also provides a welding bracket used for the above method, the welding bracket is used for placing an operator's hand to make the welding more stable, makethe controlled welding accuracy higher and ensure the welding quality.