The invention relates to the technical field of blowers, in particular to an expansion and transformation method for an axial-flow blower. The method comprises the steps of splitting the axial-flow blower; determining parameters of flow, an exhaust pressure and total capacity of the transformed axial-flow blower; calculating parameters of a stage number, a blower rotor hub diameter, flow channel parameters, and moving cascades and static cascades of all stages of the transformed axial-flow blower; transforming the stage number, the blower rotor hub diameter, the flow channel parameters, the moving cascades and the static cascades according to the calculated parameters of the stage number, the blower rotor hub diameter, the flow channel parameters, and the moving cascades and the static cascades of all the stages of the transformed axial-flow blower; replacing a static blade cylinder, an adjusting cylinder and a pressure expander of the axial-flow blower; and analyzing the yield strength of the moving cascades and the static cascades of the transformed axial-flow blower through a simulation experiment. According to the expansion and transformation method for the axial-flow blower, provided by the invention, effective utilization of idle blowers due to the factors such as blast furnace production halt, upgrading and the like is realized, so that resource waste is avoided.