The AgI seeding experiments using seeding aircraft were carried out to enhance precipitation at the upriver catchments of the Miyun reservoir from June 2004 to July 2005. According to the regular and continuous measurements at two sampling spots located at the entrance of the Bai River and the reservoir, the effects of seeding precipitation on Ag⁺ and other chemical compositions of the water in the Miyun reservoir are studied. It is shown that the constituent concentrations of the water in the reservoir during the seeding period are lower than those during non-seeding period. There is obvious monthly change of the Ag⁺ concentration. It shows that the minimum occurred during seeding period and the maximum during non-seeding period. The results suggest that the enhancing precipitation by seeding does not effect the Ag⁺ concentration in the Miyun reservoir.