Diffractive optical elements can greatly improve the performance of optical imaging systems by achieving wideband high diffraction efficiency with bilayer diffractive optical elements. The conventional design method for bilayer diffractive optical elements (DOEs) utilizes two specific design wavelengths to optimize the diffraction efficiency. However, this method may not provide enough viable solutions when the required diffraction efficiency cannot be achieved at these two wavelengths. In this paper, we propose a direct search method that can enhance the diffraction efficiency of bilayer DOEs further. We achieve higher diffraction efficiency and lower microstructure heights of double-layer discs with linear optics (DLDOEs) across a wide range of fields of view and working wavebands. A detailed comparison of a proposed method with two wavelength method is presented. When the period width is 100 μm, our method can reduce the microstructural heights of the first and second layers of DLDOEs by 22% and 25%, respectively. This method enables us to produce diffractive optical elements with higher diffraction efficiency and lighter weight. Our direct search method provides a fundamental framework for the parametric fabrication of diffractive optical components and enables their application in advanced optical imaging systems.