Abstract: The study of the correlation between compression characteristics and pore size distributions (PSDs) is one of the ways to explore the macroscopic and microscopic relationship of soils. To study the pore structure at different depths with similar initial void ratio and different compression characteristics and the pore structure changes at all different depths after undergoing a loading and unloading, a series of compression and mercury intrusion porosimetry (MIP) tests were simultaneously conducted on the undisturbed Yangzhou clayey soils at different depths. The test results show that the PSD of the undisturbed Yangzhou clayey soils at depth from 3 to 21 m is unimodal. The pore-size mainly distributes between 0.2 and 5 μm. The compression performance is closely related to the PSD, and the more concentrated the PSD, the smaller the compressibility. The soil samples at depths 12, 15 and 18 m have wider PSD, much more small pores, greater compressibility and stronger structure than other depths. The compressibility at different depths with similar initial void ratio is different with different PSDs. After undergoing a loading and unloading, the proportion of the medium pores in each soil layer decreases, the PSD moves toward the small pore diameter, and the proportion of the large pores does not change much, while the cumulative pore volume decreases at depths 12, 15 and 18 m are larger, so the decrease in the proportion of the medium pores at the 12, 15 and 18 m soil samples is more pronounced. The research results are of reference value for the study of the correlation between the engineering characteristics and microstructure of clayey soils.