Abstract: Coal is the dominant energy source in China and serves as a cornerstone for ensuring national energy security. Low-rank coal accounts for 55% of China’s total coal resources and mainly includes lignite, long-flame coal, non-caking coal, and weakly caking coal. Due to its low degree of coalification, well-developed pore structure, and abundant oxygen-containing functional groups, high-moisture low-rank coal exhibits strong hydrophilicity, with a moisture content generally ranging from 20% to 60%, thereby reducing the efficiency of combustion, conversion, and storage and transportation. Dehydration is a key upstream technology for improving the quality and utilization efficiency of high-moisture low-rank coal. However, conventional evaporative drying suffers from low heat and mass transfer efficiency, restricted internal moisture migration, a high risk of localized overheating, and high specific energy consumption for moisture removal. Therefore, theoretical and technological research on safe, efficient, and low-energy-consumption dehydration of high-moisture low-rank coal is urgently needed. Taking the classification of moisture occurrence states in low-rank coal as the starting point, this study reviews the effects of physicochemical structures, particularly pore structure and oxygen-containing functional groups, on moisture occurrence in high-moisture low-rank coal, and summarizes moisture migration behaviors and kinetic models during evaporative drying. The key scientific issues and technical bottlenecks associated with thermal stability and safety control, as well as restricted heat and mass transfer during dehydration and upgrading, are identified. The results indicate that the dehydration of low-rank coal is governed by moisture occurrence states and coal–water interactions. Free-water evaporation dominates the early stage of drying, whereas internal diffusion and desorption of adsorbed water become the major limiting mechanisms at the later stage. To address the process-intensification challenges in dehydration and upgrading, various methods, including microwave/radio-frequency, infrared radiation, vibration/pulsation, steam thermo-pressure transient dehydration, and hybrid processes, are systematically reviewed, and their mechanisms of interaction with moisture in different occurrence states are summarized. Microwave drying selectively heats internal moisture, providing volumetric heat sources and enhancing heat and mass transfer. Infrared radiation, superheated steam, and high-temperature hot air increase the heat and mass transfer coefficients at the external boundary and enhance surface evaporation. The introduction of vibration, pulsation, and airflow energy reduces particle agglomeration, improves bed fluidization, and promotes heat and mass transfer. Steam flash drying integrates steam condensation heat transfer, transient pressure-release flash evaporation, and physicochemical structural reconstruction, enabling rapid and safe dehydration under a steam atmosphere while suppressing moisture re-adsorption. On this basis, a whole-process synergistic optimization pathway based on “moisture occurrence-energy input–heat and mass transfer-safety boundary–product stability” is proposed, and a comprehensive evaluation system integrating technical, economic, and safety considerations is established for dehydration. For mild drying and upgrading, the development of stable and low-energy-consumption hot-air drying technologies with improved process control is suggested. For deep dehydration of high-moisture low-rank coal, further development of multi-energy-field hybrid drying, steam flash drying, and waste-heat recovery technologies for wide-size-range and large-scale coal processing is proposed. This study provides a reference for the theoretical investigation and process optimization of safe and efficient dehydration and upgrading of high-moisture low-rank coal.