The space evolution process of ground fluid anomalies before five medium strong earthquakes of northern part of North China is systematically studied. The anomalous migration feature is analyzed. On the basis of the migration feature as well as relation between anomalous time and epicentral distance, five signs and three steps for predicting risk region of strong earthquake are given,which are tested by three earthquakes. The results show it is possible to predict risk region of coming strong earthquake to a certain extent by using space evolution features of ground fluid anomalies.