Because they can provide a unique light-matter interface, various vortex beams carrying net orbital angular momentum have become a hot issue in structured light science. With the developing of the field, “perfect flattop vortex beams" that have both homogeneous intensity and phase distribution are particularly desired in the field of optical tweezers and nonlinear optics. Regarding to the challenge, based on super-Gaussian function, a complex-amplitude-computed holography for generating the “perfect flattop vortex beams" is theoretically proposed, the principle is experimentally proofed in a digital Fourier transform system based on a phase-only spatial light modulator, and the method to obtain the beam with a smooth vortex singularity in a finite-aperture system is mainly focused on.