The analytical expression for the propagation of higher-order Bessel beams through an aperture paraxial optical ABCD system was derived,which was used to study the evolution of phase singularities of a higher-order Bessel beam diffracted by an aperture.It shows that there always exists an optical vortex at the center of the diffracted higher-order Bessel beams and the topological change is conserved during the propagation,but the size of the vortex core varies with the aperture radius,propagation distance and beam number.Depending on the aperture radius and propagation distance,the circular edge dislocations may vanish or appear.