By using a three-dimensional convective cloud model with the AgI seeding scheme, sensitivity simulations are conducted with various graupel densities and fall velocities. These parameters influence seven microphysics processes of graupel particles. Numerical simulations show that these parameters affect rainfall amount as much as 4.9%. The relationship between graupel fall velocities and wind updrafts are modified after seeding, and the values of collection of cloud water by graupel, collection of ice by graupel, and melting of graupel to rain water are influenced. When increasing only graupel density, graupel mixing ratios are increased significantly. Graupel density and fall speed parameter also change the rainfall efficiency of both seeding and natural clouds. Increasing the graupel density along with the fall velocity parameter results in relatively high rainfall efficiency, and their seeding effects are only 15% rather than the 25% noted in control seeding simulation. Therefore, in the simulation of the rime density of convective clouds, both the graupel density and fall velocity parameter should be increased; otherwise, the seeding effect will be significantly enlarged.