Abstract: Based on the lithological homogeneity of claystones, logging data of time difference of acoustic wave have been used to study the porosity and compaction of claystones. The claystones in the continental basins of Eastern China are often sand-bearing. The readings of time difference can be strongly affectted by the variation in silt content of claystones. This is likely being neglectted, because it can not be identified from the information of natural potential logy. There are possibilities of error in selecting values of time difference and normal trend lines, and in geological explaination as well. The authors analyse these problems using acoustic log and actual information from the Qibei Depression and propose the right way to solve such problems.