Grain boundaries are one of the common defects in metallic materials and strongly affect the mechanical properties of metals. In response to the urgent demand for high strength and damage resistance of metallic materials in engineering applications, this paper takes the properties of grain boundaries and corresponding mechanical properties as examples to systematically review the digital and intelligent research progress of the microstructure and mechanical properties of metallic materials. This review elaborates on the closed−loop research paradigm of "high−throughput computing − theoretical model − machine learning and large language model". In detail, the high−throughput computing platform generates material data in batches through multi−scale computing, forming the large database. Based on the large database, combined with the classical thermodynamic/dynamic models of materials science and the bonding theories of metal physics, descriptors and theoretical models are constructed to establish the quantitative structure−activity relationship between microstructure and macroscopic mechanical properties. Machine learning can be used for rapid prediction of material properties. They can also integrate descriptors with theoretical models to solve the "black box" problem, thereby guiding theoretical calculations and experimental studies. Large−language models can be trained on massive materials science texts, demonstrating powerful cross−disciplinary knowledge integration and generation capabilities, and can serve as efficient intelligent research assistants to assist in material discovery and design. Finally, we also look forward to the development of this field towards the deep integration of physical constraint embedding and autonomous scientific discovery. We also propose the key challenges, such as data quality, theoretical universality, model transferability, and "Hallucination" of the large−language models. All these reviews provide a systematic theoretical reference for the digital and intelligent research on the grain boundary properties and corresponding mechanical properties of metallic materials, as well as for the design of high−performance metallic materials.