Abstract: Earthquake preparation gaps occrred before two moderate-strong earthquakes which occurred recently in the Sorthem Yellow sea. And they were locaed in the same background gap early or late and a similar process of dynamic development. These phenomena may be related with the cluster of strong seismic activity in the Sorthern Yellow Sea area. A carefull study of the relationship between the background gap and earthquake preparation gaps may be a way by which long-term earthquake prediction may be transited to midttcrm prediction.#br#The seismic activity pauerns of the two. moderatestrong earthquakes which occurred reccnliy in the Sorlhern Yellow Sea have a good return property. This has a practical signiticance for earthquake detection in the future in this area.