Abstract: Land subsidence is one of most main geological disasters in the Yangtze river delta economic region. With the ban of Suzhou-Wuxi-Changzhou area groundwater exploitation, the mainly compression deformation of soil is from aquitard at present. This paper took the No.06 drilling from Guangming village, Wuxi city, for an example. The pore size distribution of soil was analyzed based on mercury intrusion porosimetrytest and the relation between the pore of cohesive soil and land subsidence was studied. According to the result of mercury intrusion porosimetry, an evaluation method of aquitard compression potential was proposed using the concept of macro-pore porosity emip. The index emip can evaluate the compression potential of aquitard. The potential of aquitard compression shows a tendency: Ⅰ-1 aquitard Ⅱ aquitard Ⅰ-2 aquitard Ⅰ-3 aquitard. The result is consistent with the compression parameter and the microstructure of soil samples. So it is a effective way to evaluate the compression potential of aquitard stratum.