Abstract: The survey and evaluation of fault and its activity is an important part of geotechnical engineering investigation.Gas geochemistry method can be used in the fault investigaton.Study on fault gases could help us to locate the faults,especially for the buried fault,to determine the fault's scale,attitude,cut depth,and to analyze the activity of fault.Meanwhile,time-spatial variation fault gas field could provide a great amount of additional imfomation for site sesmic risk analysis,calibrition of seismic intensity and seismic microzoning.