A comprehensive field observation was conducted in the Qinghai artificial weather modification experiment base located in Henan County, Qinghai Province, China, in September 2002. On the basis of ice nucleus data obtained by this field observation, combined with two commonly used ice nucleus data, the effects of three different atmospheric ice nucleus spectra on cloud seeding in convective storm clouds are examined in this paper by using the fully elastic three-dimensional convective storm model (IAP-CSM3D). The differences in cloud-seeding trajectories of RYI-6300- and WR-1B-type rockets commonly used by domestic weather departments are considered. The simulation results show that the ice nucleus spectrum has a significant impact on the macro- and microstructures of strong convective clouds. Moreover, the seeding effects of these clouds differ significantly with various ice nucleus spectra. When the ice nucleus number concentration is low at high-temperature levels and high at low-temperature levels in the atmospheric environment, seeding in convective storms will lead to excessive ice crystals, which has a negative effect on the precipitation of convective storm clouds. When the ice nucleus number concentration is higher at high-temperature levels and lower at low-temperature levels in the environment, the seeding effect in convective storm clouds is the greatest. The physical explanations for these differences are given in this paper. When ice nucleus spectra were observed in the Qinghai experiment area, rocket seeding in convective storm clouds had a certain effect in rain enhancement. A clear understanding of the background status of ice nuclei is critical for proper assessment of cloud-seeding effects when conducting artificial weather modification experiments.