Provided is a method of austenite grain refinement and re-nanocrystallization acceleration for nano-bainitic steel. The invention relates to the field of high-strength steel welding, in particular to a method of first conducting plastic deformation, then conducting static recrystallization, refining austenite grains and accelerating re-nanocrystallization. The method is used for solving the problem that time is long and industrialized application is difficult in the re-nanocrystallization welding process of the existing nano-bainitic steel. According to the method, welding with impact rotation is adopted in an automatic welding device, large amount of plastic deformation happens to high temperature metal of a weld joint and a heat effect area, before the austenite grains are cooled down to martensite transformation temperature, static recrystallization happens to the deformed metal through a method of flame heating, the austenite grains is refined, and re-nanocrystallization time is shortened.