Qikou sag is an important oil- bearing sag in Bohai Bay basin，and there are many fault- related traps in the sag. Under the action of multi- stage tectonic movement, four groups of azimuth faults are developed in the study area.Previous studies have analyzed and studied the role of faults in the oil- gas accumulation process from different perspectives，but most of them are qualitative studies.In this paper，by means of structural sequence interface，growth index，fault displacement- buried depth curve and other research methods，the fault activity parameter system，evaluation criteria，evaluation process and evaluation technology were systematically established，and the qualitative evaluation was changed to quantitative evaluation.The main active periods of the Paleogene faults in Qikou sag are the sedimentary periods of Es3 and Es1- Ed formation. During the sedimentary period of Es3- Es2, affected by the NW- NE extension, NE- NEE trending faults began to develop.During the sedimentary period of Es1- Ed, the direction of regional extension has changed to nearly NS,and a large number of nearly EW trending faults were developed. Combined with the law of fault distribution,the sag was divided into three structural layers from bottom to top: the prophase rifting layer，the rifting layer and the post rifting layer.The period of rifting is further divided into SR I and SR II. Through the determination of the active characteristics of faults in Qikou sag, it is found that the activities of faults in different historical periods have obvious controlling effects on the formation of sag, the evolution of traps and the effectiveness of traps.The activity of faults in different historical periods controlled the formation and distribution of small subsags controlled by faults，and the migration law of the sag is controlled by the change of stress field and fault strike. In the process of segmented growth and connection of adjacent synthetic faults, the position of the segmented growth point of upper wall can form local structural high points, thus forming traps related to synthetic faults.The matching relationship between the formation time of fault related traps and hydrocarbon generation and expulsion period is an important factor affecting the effectiveness of traps.