The realization and stable operating of Continuous Rotating Detonation (CRD) Engine fueled by hydrocarbon and air is still a problem deserving to be settled. In order to optimize the detonation combustion organization in the annular combustor, an especial cavity structure in the inner cylinder is firstly proposed in this paper. Series of experiments have been conducted for investigating the effect of cavity structure. The results show that ethylene-air CRD has been realized in the annular combustor with cavity. CRD waves propagate steadily with higher pressure and propagation velocity in the larger operating range. The cavity contributes to the propagation mode transformation from two-waves in hetero-rotating mode to two-waves in homo-rotating mode. In the cavity combustor, the propagation velocity is 1228.68 m/s on stoichiometric equivalence ratio (ER) accounting for 67.4% of the corresponding CJ velocity. The permanent flame stabilized in re-circulation zone works as the pilot flame, which has been verified by high-speed photograph images. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.