The juncture of Shanxi,Hebei,and Inner Mongolia is located at the border area of the North China Block,Ordos Block,and Yanshan Block.The seismicity of this area,which is affected by the change in the tectonic stress,is related to future moderately strong earthquakes.The earthquake prediction index extracted from the observation data is a parameter with a certain physical significance,which has some degree of abnormal changes before an earthquake.The construction of the earthquake prediction index system is one of the most effective prediction methods in the empirical prediction stage.The earthquake frequency,which reflects the changes in the seismicity level and stress level,is a commonly used earthquake prediction index.Since 2019,there has been a significant enhancement of M L ＞3.0 earthquakes in the border area of Shanxi,Hebei,and Inner Mongolia.To evaluate the earthquake precursor significance of the seismicity in this area and build an effective prediction method, the enhanced area was selected as the window of earthquake frequency, and the annual moving frequency of M _L ＞3.0 earthquakes was taken as the prediction index. The optimal prediction rule was determined by tracing back the seismicity before previous M _L ＞5.0 earthquakes. Through a spatial scanning of the parameters of the prediction rule and taking the R value as the objective function, the prediction window length and threshold were finally determined to be 2 years and 14 times, respectively. The earthquake frequency prediction index for the proposed rule has a good prediction effect and high reliability. Keywords: seismicity enhancement; prediction efficiency; juncture area of Shanxi, Hebei and In-