Superplastic forming method for hollow part with thickness step

The invention provides a superplastic forming method for a hollow part with thickness steps, which comprises the following steps: a plurality of plates are subjected to diffusion connection to form a superplastic forming blank, the superplastic forming blank is provided with a hollow area for being filled with high-pressure gas and a solid area for realizing diffusion connection, and N thickness steps are formed in the hollow area; and according to the forming mathematical model of the hollow part, designing N superplastic forming dies in one-to-one correspondence with the N thickness steps. The multiple superplastic forming dies are designed and machined on the basis of the forming digital model of the hollow part, superplastic forming is conducted on all the thickness steps in sequence from thick to thin through the multiple superplastic forming dies, all the thickness steps are thinned in sequence from thick to thin, the thickness gradient difference between all the thickness steps is reduced, and the mach