Anomalous character of radon content in Liaogu-1 well before the Ningjin M_S5.8 earthquake on November 9,1981 and the Heze M_S5.9 earthquake on November 7,1983 are analysed.Radon content in the well has gone up by a wide margin 5~10 days before the earthquakes.The earthquakes occurred during radon content dropping.Therefore,the anomalous changes of radon content of the well can be regarded as a short-impending prediction index.