Based on the GIS secondary development techniques VB (Visual Basic) and MO (Map Objects), an applicative method is proposed, that is, the scope, area and precipitation volume of an irregular influence area of cloud seeding catalytic agent during aircraft rain enhancement activity is calculated objectively while considering the two dimensional line source diffusion equation. This method is applied in the technique system on the statistical assessment on aircraft rain enhancement effect conducted by CA FCM method (Cluster Analysis based Floating Control historical regression Method). A real case of aircraft rain enhancement activity in Jilin Province is evaluated and its results are discussed to introduce the specific application.