Using the subordinate function method, the observation date of radon in No. 22 well at Wushan station from 1984 to 2003 are analyzed. Five Middle-term anomalies on the curves of subordinate function are found, and 4 of the anomalies corresponded with earthquake （Ms≥5.8） in Gansu province and adjacent regions. With this the relationship between the anomaly and earthquake, the feature of anomaly are discussed. The method and criterion of time prediction for strong and moderate-strong earthquake are obtained from the amonaly of radon.