Seeding effect evaluation is focused on whether the clouds and precipitation produced the expected significant changes after the cloud seeding, which is manifested in the process of macro and micro changes, thus it is necessary to learn something about cloud microphysical characteristics after cloud seeding. Based on the PMS data of an artificial precipitation in a convective line with trailing stratiform cloud system in Hebei Province on April 18, 2009, the cloud microphysical characteristics are studied. The results indicate that: accompanied by a significant reduction of the liquid water content after seeding, the average particle diameter increases from 20.4 μm to 23.9 μm; the spectrums of cloud particles have also undergone great changes in the structure. Simultaneously, the number of ice crystals reduces, but the size of precipitation particles increases significantly; in the cloudseeding affected zone on the ground an hour later, the accumulated rainfall reaches the maximum.