Abstract: Determination of thick layers is an important part of seismic inter pretation.This paper discusses thickness cal-culation of layers with steep dip by using the15°empirical method,analyzes the error of bedding flattening co rrection method,and discusses the geologic conditions for utilization of the fl attening method.Correction to the isopach map of T 12 4 layer in a basin with this method had achieved remark-able effects.