A silver iodide (AgI) cloud-seeding parameterization has been implemented into the Thompson microphysics scheme of the WRF model to investigate cloud-seeding effects during the opening ceremony of the Nanjing 2014 Youth Olympics Games. The results showed that the surface precipitation was decreased due to seeding, and the subcloud dry layer played an important role in modifying seeding effects. The low-relative-humidity environment was favorable for rain suppression by cloud seeding, but the situation reversed in high-relative humidity environment. The seeding enhanced the formation of snow but weakened the growth of snow, especially deposition growth. As a result, the concentration of snow increased but the size of snow decreased. The snow melted and turned into a large number of small raindrops, which evaporated easily, resulting in less precipitation on the ground.