In the exploration of the hidden Haihe fault,radon and mercury in soil gas were measured by using FG-3017 radon detector and XG-4 mercury analyzer.In this paper,based on the measurement results of 12 fault gas profiles,and integrating with the exploration results of artificial seismic prospecting,the relationship between anomalous site of fault gas and fault location is analyzed.Using the relationship between anomalous strength of fault gas and fault activity,the activity of Haihe fault is studied,thus the location and activity segmentation of the Haihe fault in Tianjin region are presented.This study shows that the method of fault gas detection can not only identify the preliminary location of fault,but also make preliminary segmentation of fault activity.The fault detected by the method of fault gas measurement is shown as a band.Through contrasting with exploration results of artificial seismic prospecting and analyzing,we find that the fault is located inside the band.According to the measurements of soil gas radon,the Haihe fault can be divided into east and west segments and the activity of the east segment of Haihe fault is stronger than that of the west segment.This is only a relative result,and it is difficult to judge whether the fault is active or not with this result. In the exploration of the hidden Haihe fault, radon and mercury in soil gas were measured by using FG-3017 radon detector and XG-4 mercury analyzer. In this paper, based on the measurement results of 12 fault gas profiles, and integrating with the exploration results of artificial seismic prospecting, the relationship between anomalous site of fault gas and fault location is analyzed. Use the relationship between anomalous strength of fault gas and fault activity, the activity of Haihe fault is studied, thus the location and activity segmentation of the Haihe fault in Tianjin region are.This study shows that the method of fault gas detection can not only identify the preliminary location of fault, but also make preliminary segmentation of fault activity. The fault detected by the method of fault gas measurement is displayed as a band.Through contrasting with exploration results of artificial seismic prospecting and analyzing, we find that the fault is located inside the band. According to to the measurements of soil gas radon, the Haihe fault can be divided into east and west segments and the activity of the east segment of Haihe fault is stronger than that of the west segment. This is only a relative result, and it is difficult to judge whether the fault is active or not with this result.