Exploration is undertaken of the pairing of climatically statistical Z-I probabilities and Z-I relation based on April June statistics over 200 km around Changsha. Evidence suggests that the rainfall pattern is broadly similar in the wet season and the obtained Z-I relation is applicable to the study region; the relationship, when used with the ATi method, is able to further improve the measurement accuracy from a single radar set. Also, the technique is independent of a automatic surface rainfall measuring network.