Based on the reasonable simulation of cold frontal precipitation event in South China on 31 March 2004, seeding effects through directly adding ice crystals in the simulated clouds are studied. The results show that after seeding 30 minutes surface rainfall started to increase, after seeding 80 minutes the Net Rainfall Increment (NRI) reached a peak, then after 120 minutes NRI decreased to a minimum. The seeded cloud moved southeasterly with the natural precipitating band moving, and the seeded cloud influenced the neighboring clouds, which caused the seeding effects last about 10 hours, then dissipated with the natural clouds dissipating. The seeding effects conformed to the hypothesis of “downwind extra-area effects”. Supercooled raindrops were quickly transferred into graupels after artificial ice crystals were injected. Then graupels grew mainly through riming supercooled cloud water and collecting raindrops. Thus precipitation developed in advance, then the melting of graupels caused the surface rainfall increase. The release of a large quantity of fusion latent heat made the temperature in cloud increase, strengthened the updrafts, which indicated that “static seeding” and “dynamic seeding” are correlative each other. The seeding effects of adding ice crystals in the cloud developing stage were better than those in the cloud mature stage. The difference of NRI caused only by the seeding agent dose in different seeding experiments was relatively small.