Advection cooling fog (hereafter advection fog) occurs frequently over the northwestern Pacific during summer, posing serious threats to maritime transportation safety. However, owing to an inadequate representation of cloud microphysical processes, current numerical models still exhibit limited skill in simulating and forecasting sea fog. In this study, comparative large-eddy simulations are performed for the same northwestern Pacific advection fog case using the University of California, Los Angeles Large-Eddy Simulation model (UCLALES) with a bulk cloud microphysics scheme and its configuration coupled with the Sectional Aerosol module for Large-Scale Applications (UCLALES–SALSA). The impacts of explicitly resolving cloud microphysical processes on advection fog simulations are systematically examined. The results show that, relative to the UCLALES experiment, the evolution of liquid water content and liquid water path is significantly suppressed in the UCLALES–SALSA experiment. This difference mainly arises from the microphysics module, which transports fog-top liquid water downward through droplet sedimentation and promotes substantial evaporation near the fog base. In addition, the inclusion of the microphysics module shifts the peak of the droplet size distribution toward larger diameters and enhances the contribution of large droplets to the droplet number concentration. This spectral adjustment is associated with more pronounced visibility fluctuations during the maintenance stage of the fog and can lead to an increase in droplet effective radius even under conditions of relatively weak liquid water content variability. Through a large-eddy simulation framework, this study quantitatively demonstrates how cloud microphysical processes regulate the vertical structure of liquid water and visibility variations in advection fog. The results highlight that an explicit representation of key microphysical processes, including aerosol activation and fog droplet sedimentation, is crucial for improving the numerical simulation of sea fog. These results provide new high-resolution modeling insights into the microphysical controls of advection fog over the northwestern Pacific and offer a valuable reference for the development of more reliable fog forecasting models.