Abstract: Natural precipitation process can be divided into two stages, i.e., cloud formation stage and precipitation formation stage. Although weather modification can affect the precipitation formation stage, the key factors dominating rainfall are the lifting movement which induces cloud formation and the water vapor content in the lifting air mass. Choice on the cloud seeding location and time in weather modification depends on if the operation can benefit the lifting movement. Thus, as measurements of macro- and micro-physics conditions are strengthened, measurements on the lifting movement and the water vapor in the lifting air mass should be greatly strengthened as well. At the same time, numerical simulation research should consider dynamic fields and water vapor fields, which control the development of the rainfall system.