Abstract:Theoretical model calculation shows that the distinquishable bed thickness esti- mated using seismic interval transit time is 1/8一1/4 wave length. The extensive dolomite Carboniferous system in east Sichuan Province underlies the mudstone of the bottom Yangxin series and overlies thick sandy mudstone in Silurian system,be- coming a good seismic reflector. Synthetic seismograms at several wells coincide with corresponding real seismic data very well. The bed thickness calculated using interval transit time of synthetic seismogram is equivalent to drilled thickness. It is possible,therefore,to derive bed thickness (thicker than tuning thickness)from seis- mic interval transit time.