Crystalline solids, which often possess distinguished mechanical properties among distinct orientations, may be potentially further recombined into various composite materials as an effective design strategy. [1][2][3][4][5][6] Among different types of composite design methods, better mechanical properties may be achieved by making use of the anisotropy and grain boundary effects seen in nanomaterials. [7][8][9] Considering any given space of a material, there is potential for microstructural design to improve its performance. However, in most cases, the cost of simulation or experiment will rapidly increase along with the daunting complexity of the sheer number of possible combinations within a given design space, and therefore the traditional process of composite design with experiment or simulation on crystalline solids is not capable of discovering new composite materials in a productive way. Here, the use of artificial intelligence (AI) methods [10,11] can be a powerful way to accelerate the discovery process [12][13][14][15][16][17][18][19][20][21] and, as we will show in this article, can also provide important mechanistic insights into the structure-property relationships. As such it complements other multiscale models in our quest to better understand how materials perform under extreme conditions.We adopt a framework that combines a deep learning (DL) model with a genetic algorithm (GA) [12,15,21] to rapidly search and generate composite materials on demand-simulating "nature's evolution paradigm" [19,22] -to achieve different mechanical properties, a process that enables us to realize "inverse design" through a continuous assessment of variations in design suggestions. Figure 1 shows a summary view of the method reported in this study. The deep learning model in this framework serves as a surrogate model for molecular dynamics (MD) simulation to help us obtain certain properties much faster, [15] offering a novel way to discover key mechanical feature of a material. As a result, the GA can perform a computationally efficient optimization of polycrystalline composites by using the DL-derived simulation results as feedback. Overall, the goal of this framework is to automatically determine optimized polycrystalline solid design