The diffraction efficiency under oblique incidence is low in traditional optimization methods for Double-Layer Diffraction Optical Elements(DLDOEs).Based on the model of theoretical relationships of diffraction efficiency with incident angles and wavelengths for DLDOE, an angle-optimized design method is proposed. By analyzing the influence of different incident angles and micro-structure heights on diffraction efficiency in the designing process, optimal micro-structure heights are selected, which significantly enhance the diffraction efficiency at large field-of-view.In order to validate the above theory, the proposed angle-optimized designing method is applied alongside the method of equal diffraction efficiency under long and short wavelengths, and the bandwidth-integrated average diffraction efficiency maximization method, and the DLDOE in both the visible light and infrared spectrum are designed.The results demonstrate that the angle-optimized design method can effectively increase the angular bandwidth-integrated average diffraction efficiency of DLDOE, thereby enhancing the imaging quality of optical systems.Finally, based on the angle-optimized designing method, a long-focus hybrid refraction-diffraction system is designed, which achieves high image quality with high diffraction efficiency.