Abstract: Seismic data processing and interpretation will involve the datum level problem, and the influence of different datum levels on the results is different. The datum defined by conventional static correction method can meet the requirements of seismic data processing, but there are some deficiencies, such as time?depth conversion of the datum, error between smooth surface and CMP datum, etc. In this paper, back?calculation of the datum is based on the known surface structure parameter, by which not only make the static correction in line with the principle of minimum, but also allow each CMP gather to have individual horizontal datum, give the datum more accurate above?sea?level meaning, and be able to get a elevation datum from profile interpretation and structure?depth conversion for comprehensive research, while having satisfied the requirements of seismic data processing, thus avoiding the errors of CMP datum conversion in time domain. The theoretical model tests show that the structure accuracy of the depth?domain profile in this approach is obviously improved compared to the conventional datum method. It provides a powerful means for petroleum exploration in low?amplitude structures