Abstract: Effects of vortex generators on the external flows of an axisymmetric hypersonic inlet were investigated by three-dimensional CFD simulations. Effects on the flow structures and performance parameters were analyzed on two configurations, of which noses were 0.8 mm radius and 3.2 mm radius, respectively. The results show that the induced shock waves of vortex generators cause outward displacements of the external shock waves. The momentum exchanges between the near wall flows and external main flows are enhanced, which results in evident spanwise non-uniformity in the downstream flowfield. The effects of vortex generators degrade in the streamwise orientation. The pressure ratio and dynamic pressure ratio of spanwise cross sections increase at first, then the increments gradually degrade and recover to the values of no vortex generator conditions. The Mach number and the recovery coefficients of total pressure also decrease at first and gradually recover in the streamwise orientation. The parameter h, which is the ratio of vortex generator heights to the displacement thicknesses of the local boundary layers, can be used to characterize the influence intensity of vortex generators. For both configurations, variations of flowfield and performance parameters are negligible as h ≤ 1.5. The performance parameters can recover to the values of no vortex generator conditions by the inlet entrance as h ≤ 3.0.