利用调制地震方法对华北地区１９７３年以来发生的２４个ＭＬ≥５．５地震前地震调制比、地震调制比异常面积、调制地震条带和调制地震频度的异常变化进行分析，对异常类型进行分类。分析结果认为，华北地区ＭＬ≥５．５地震前地震调制比和异常面积随时间进程的起伏、调制地震频度震前数月的突然增大以及调制地震条带异常图象是显著的异常变化，可以用于对中、强地震的中期预报 By using the modulation and seismic method, the anomalous changes of the seismic modulation ratio, the anomalous area of ​​the seismic modulation ratio, the modulation seismic band and the modulation frequency before 24 ML≥5.5 earthquakes occurred in North China since 1973 were analyzed, and the types of anomalies classification. The analysis shows that the seismic modulation ratio and the anomaly area before ML ≥ 5.5 earthquakes in North China fluctuate with time, and the abrupt increase of the seismic frequency in the past few months before the earthquake and the anomalous image of the modulated seismic band are significant anomalous changes , Which can be used for medium-term forecast of moderate and strong earthquakes