The invention provides a welding process for a hot pipe, and relates to the field of pipe welding. The welding process for the hot pipe comprises the following steps: first, performing surface treatment on an evaporation section, a condensation section and a connecting pipe, respectively arranging the end part of the evaporation section and the end part of the condensation section in the two endsof the connecting pipe in a sleeving manner, and enabling liquid absorbing cores in the evaporation section and the condensation section to be in contact with each other; under the protection of nitrogen gas, welding by adopting brazing, wherein the welding parts are the parts, which are respectively matched with the evaporation section and the condensation section, of the two ends of the connecting pipe; performing residue removing treatment on a welded part and grinding the welded part; performing vacuumizing treatment on the hot pipe, injecting an evaporating liquid through an air exhaust hole under vacuum condition, and simply closing the air exhaust hole; under the protection of the nitrogen gas, brazing and closing a closing position of the air exhaust hole; and performing residue removing treatment on a brazed part of the air exhaust hole and grinding the brazed part of the air exhaust hole. The liquid absorbing capacity of the liquid absorbing cores cannot be affected by welding the hot pipe through the process provided by the invention.