The invention discloses a method for designing a hollowing-out index ultrasonic amplitude transformer, and belongs to the field of power ultrasonic amplitude transformer design. The problems that existing amplitude transformers are all designed to be of a solid structure and lack a hollow structure, and the amplification coefficient of the solid ultrasonic amplitude transformers is limited are solved. The method includes the following steps that first, the area coefficient N, resonance length l and winding indexes beta and delta are calculated; second, the displacement node x0 is also calculated; third, the amplification coefficient M is further calculated; fourth, the strain maximal point xM is calculated, and accordingly the shape factor phi is obtained; and fifth, simulation software is used for conducting numerical simulation according to the data and calculation results given from the first step to the fourth step, and design of the hollow ultrasonic amplitude transformer is optimized. The method is suitable for designing the hollowing-out index ultrasonic amplitude transformer.