Abstract: In order to understand the ability of ice nucleation of AgI hydrosol in the experiments of the weather modification, we measured the particulate spectrum of AgI hydrosol with an electron microscope. The results show: there is a little difference in the particulate spectrum of AgI hydrosol between various prescriptions, however, almost no difference has been detected in the same prescription. We taek the average spectral distribution of samples from 9 AgI hydrosol of different prescriptions and concentrations, particles of a diameter larger than 0.05μ have been found to account for 3% of total particles. If all of those particles made the ice nucleation at low temperature, the highest rate of AgI ice nucleation would be 1014/g. However, if the seeding experiments when the AgI hydrosol drops did not lend themself to the dispersion of AgI particles, the rate would be lower. Let it be supposed that, the particles of AgI hydrosol in the form of frozeri drops made clouds crystallized, the frozen drops would cause multiplication of ice crystals, which would increase the nucleation rate higher than the above estimated one.