Abstract: This article defines the natural precipitation conversion factor K as the ratio of the water vapor density ρ and precipitation Q (K=Q/ρ) and interprets the physical process of precipitation caused by rising of ground water vapor in terms of climatology and cloud precipitation physics. K reflects the weather system and rainfall conditions; it also describes the precipitation system’s thermal dynamics and the capability of the cloud microphysical processes that convert ρ into Q. A large K value indicates high efficiency for vapor conversion to precipitation, and a small K value indicates poor precipitation conditions that cause low efficiency in the process of vapor conversion to rainfall. To obtain the best effect in artificial precipitation, we should choose the area having the largest K value. This article calculates and analyzes the average K over 30 years (1951-1980) in Jilin. This can be used as a reference for choosing the proper area for operation. The regional differences in K are found to be significant. The overall distribution decreases from the southeast to the northwest, and K is the largest at Tianchi station. In addition, K varies greatly with the time distribution; it is largest in the summer, with intermediate values in spring and autumn, in that order, and a minimum in winter.