The invention provides a thermal treatment method for a formed weld joint of a drill rod. The thermal treatment method comprises the following steps that firstly, annealing treatment is carried out on a weld joint zone which is formed between a drill rod pipe body and a connector through friction welding; then the annealed drill rod is placed in air to be cooled until the drill rod is cooled to the room temperature; and finally the cooled drill rod is subjected to tempering treatment. By means of the thermal treatment method, as tempering sorbite is formed, the structure of the weld joint of the drill rod is finer, and the problem of cracks in the weld joint of the small drill rod is completely solved.