[en] Abstract Background: A water-cooled high energy double Laue crystal monochromator (DLM) will be employed on ultra-hard applications beamline to be built in phase II project at Shanghai Synchrotron Radiation Facility (SSRF). Its crystal bending performance is very important for satisfying design requirements. Purpose: This study aims to find appropriate coupled meridional and sagittal bending of the bender, to obtain optimal the monochromatic beam flux and energy resolution. Methods: The rigidity matrix of the crystal was calculated by using MATLAB. Two main factors, anisotropic elasticity of the asymmetric-cut crystal and aspect ratio, are considered to optimize the crystal bendings by finite element analysis (FEA) using ANSYS Workbench. Results & Conclusion: Analysis results show the cutting edge of crystal length and width goes along the[011] and [0-11] direction, respectively. The optimized crystal geometry is 90 mm × 40 mm × 1 mm. Furthermore, the meridional and sagittal slope errors of the crystal are 3.02 μrad and 1.25 μrad, respectively, which meet the requirements well. (authors)