Abstract：The precondition of RU line being as datum oftime-depth conversion is that the RU line is equiva-lent to the smooth line of surface elevation.Themethod was feasible in former exploration of looking for structural trap.The reasons are follows:①the surface relief is simple in previous explorationarea,RU line can approximately be as smooth lineof surface,replacement of elevation of RU line bysmooth line of surface makes little errors;②theerrors of reflection time are only a few ms or evenscores ms,having no influence on discovery of anticline structure.Present seismic exploration putshigh-resolution and high-precision as its object,sothat can find out structuralli thological oil/gasreservoir,such as structure with lower amplitude,fault,fracture and sand body, which demands data(from processing and interpretation)coming tosome precision, so can ensure the reliability of interpretation of seismic section.In that cases,it isworth to consider whether the RG line is suitablefor datum of interpretation of seismic section.Thepaper expounds in detail the relation between RGline and smooth line of surface.Its aims are show-ing the difference between RG line and smooth lineof surface elevation,the negative influence on inter-pretation precision of subsurface structure if usingRG line for datum of interpretation of seismic sec-tion and how to solve the datum of time-depth con-version.
