Abstract: Drilling well is very expensive on the sea, so the geophysics dream of finding the oil and gas directly with geophysical technology. In the structure oil and gas accumulated, seismic datas as reflection coefficient, velocity and frequency would change, the "strong reflection spot" or "weak reflection spot" is formed above the oil and gas layer and the unusualness of the low frequency and low-velocity appears. These are special symbols indicating whether there exists hydrocarbon in the structure.