High-mercury wet deposition in the southeastern United States has been noticed for many years. Previous studies came up with a theory that it was associated with high-altitude divalent mercury scavenged by convective precipitation. Given the coarse resolution of previous models (e.g., GEOS-Chem), this theory is still not fully tested. Here we employed a newly developed WRF-GEOS-Chem (WRF-GC; WRF: Weather Research Forecasting) model implemented with mercury simulation (WRF-GC-Hg v1.0). We conduct extensive model benchmarking by comparing WRF-GC with different resolutions (from 50 to 25 km) to GEOS-Chem output (4∘ × 5∘) and data from the Mercury Deposition Network (MDN) in July–September 2013. The comparison of mercury wet deposition from two models presents high-mercury wet deposition in the southeastern United States. We divided simulation results by heights (2, 4, 6, 8 km), different types of precipitation (large-scale and convective), and combinations of these two variations together and find most mercury wet deposition concentrates on higher level and is caused by convective precipitation. Therefore, we conclude that it is the deep convection that caused enhanced mercury wet deposition in the southeastern United States.