Radiative cooling at the top of fog is a crucial physical process during the evolution of fog, driving a “top-down” turbulent mixing. Therefore, the YSU (Yonsei University) scheme incorporates a module (ysu_topdown_pblmix) to represent this process. However, the influence of such “top-down” turbulent mixing on heavy fog events in the North China Plain remains unclear. This study evaluates the suitability of ysu_topdown_pblmix in simulating fog events in the North China Plain based on Himawari-8 satellite retrievals, automatic station observations, 15-layer atmospheric boundary layer gradient measurements, and 5-layer turbulence-related observations. Large-eddy simulations are also used to supplement the analysis. The investigation reveals that while ysu_topdown_pblmix overall decreases the fog area simulation scores in the North China Plain, it significantly improves the simulation of near-surface temperature, humidity, and fog boundary layer structure. This enhancement is attributed to the “top-down” turbulent mixing driven by radiative cooling at the fog top. However, the present ysu_topdown_pblmix exhibits an excessive entrainment effect, leading to too much intrusion of warm air above the fog top, resulting in rapid dissipation of fog. Sensitivity tests demonstrate that reducing the evaporative enhancement coefficient in ysu_topdown_pblmix can mitigate the strength of turbulent entrainment at the fog top, thereby improving the simulation of fog events. These findings suggest that incorporating ysu_topdown_pblmix is necessary for numerical simulations of heavy fog events in the North China Plain, but further refinement of relevant parameters is required.