Weather modification (rain enhancement, hail suppression, fog clearing, etc.) is introduced in this paper, including the basic scientific principle, history of development, present status, scientific-technical progress, scope of activities, increasing demand, organization, etc. , in China and abroad. A typical operational system of weather modification in China is described, which consists of monitoring and forecasting of weather and cloud, seeding technology (conception model, seeding criteria, effective agent, delivery system) ,numerical modeling, communication-commanding and evaluating systems. The importance of scientific-technical research system is emphasized. The main aspects of research on the concerned applied sciences and technical development are proposed. The important role of long-term stable scientific demonstrative experiments is explained. The direction of further development in this field is also suggested.