The invention relates to the technical field of welding and particularly provides a technique of repairing crack and erosion regions of a cobalt-based high-temperature alloy flame tube by welding. Thetechnique includes a flame tube repairing process: removing flame tube rivets, separating parts, performing shot blasting, polishing crack and erosion regions and their perimeters, performing net shaping repairing by welding, manufacturing a coating layer, thermally treating in vacuum, and assembly; first, the flame tube is removed, the parts are subjected to shot blasting, and the crack and erosion regions are cleaned and polished; second, net shaping by welding is utilized to repair the crack and erosion regions of the flame tube, and the parts are dressed after repairing; third, the coating layer is manufactured for a workpiece; the parts of the flame tube are thermally treated in a vacuum furnace; assembly is performed at last. The technique can provide effective repairing for the crack and erosion regions of the flame tube, meets the repairing need of the flame tube and provides extended life for the flame tube.