The orbital angular momentum propagated by a vortex beam is very important in free-space optical communication. In this study， a soft-edged aperture was used to improve the orbital angular momentum detection technology of a vortex beam based on aperture diffraction. The Fresnel diffraction of soft-edged apertures has a certain degree of convergence compared with hard-edged apertures. This can increase the relative intensity of the primary bright spots to the secondary bright spots in far-field diffraction distribution， thereby improving the recognizability of the primary bright spots and expanding the range of orbital angular momentum based on aperture diffraction. The best detection effect was achieved using the primary and secondary bright spots intensity contrast values in far-field diffraction and the peak and trough intensities average contrast values in the primary bright spot area under the appropriate super-gaussian orders. By combining theoretical simulations and experiments， it can be seen that the use of rectangular soft-edged apertures can further increase the detection range of vortex optical topological charges from the 20th order to the 30th order， and the use of triangular soft-edged apertures can increase the detection range from the ±10th order to ±20th order.