Aiming at the cracks of welding joint for 12Cr1MoVG steel header links of the grade I desuperheater of boilers in the ultra-supercritical units, the weldability of 12Cr1MoVG steel and technical difficulties of crack repair welding for the header links are discussed in the paper. The welding conditions and the post-weld heat treatment in the entire process from the pre-welding treatment to welding inspection are introduced. It is shown from the results of welding inspection that the repair welding quality of welding joint for 12Cr1MoVG steel header links in desuperheater can be ensured by the repair welding process.