The research attention and detecting methods on the fault in the seismic safety evaluation and petroleum exploration are compared in this paper, including the activity age, location, size, attitude, characteristic of the fault etc. In the seismic safety evaluation, it pays more attention to the faults in the surface and shallow layers, and the activity age, which is the important factor to judge the earthquake magnitude, but in the petroleum exploration it pays more attention on the faults in the deeper, which is the key to form the fault-block traps or not. The research methods include geological outcrop investigation, gravity survey, geomagnetic survey, seismic survey, drilling-hole etc.