Abstract: Abstract: Direct air capture (DAC) technology is essential for achieving carbon neutrality. Adsorption-based DAC is a promising approach due to its high CO2 selectivity and practical implementation potential. However, a major challenge is the high energy requirement and cost of capturing CO2 from air with its ultra-low concentration of approximately 400 ppm and dynamic temperature and humidity variations. Multiscale modeling has become a crucial systematic framework for analyzing this complex problem. It provides a comprehensive methodology spanning from microscopic mechanisms to macroscopic systems. First, Monte Carlo and molecular dynamics simulations are used to study adsorption mechanisms and predict fundamental material properties. Second, models describing gas adsorption and reaction rates are combined with equations for mass and energy transport to simulate the dynamic capture process in units such as fixed-bed contactors. Finally, simulations of cyclic processes like temperature vacuum swing adsorption are integrated with detailed energy calculations and techno-economic analysis to assess overall performance and the levelized cost per ton of CO2 captured. At the system integration level, current research challenges are concentrated on developing accurate models that reflect real atmospheric conditions and creating operating strategies for the dynamic integration of DAC with intermittent renewable power. Looking forward, advancing intelligent modeling by deeply integrating physics-based models with data-driven methods is key to driving adsorption-based DAC technology toward cost-effective, large-scale applications.