Abstract: The structure and main technical characteristics of the automatic Instrument HWF-1 type, for downhole measuring the intensity of γ-ray, are described in the present paper. The instrument was designed at first to be specially used for earthquake prediction, it can also be used to measure water temperature. The experimentally observed data by this instrument at the flowing well in Nanchang clty, Jiangxi Province, has been analyzed. The intensity values of γ-ray in the water of the well showed obvious changes, which are effected by many factors such as rainfall. By using the method of first order def-ference to determin the anomaly of the values of γ-ray intensity, the anomaly of γ-ray intensity is obvious before the occurrence of moderately strong earthquake, therefore it is considered that the measurement of γ-ray intensity is a useful and new method in the observation of hydrogeoohemistry.