Mercury porosimetry (MP) is one of the analytical methods to measure the porosity and the pore size distribution of porous materials. We have developed a new method of digital mercury porosimetry (DMP) for characterizing the porous structure by simulating the measuring processes of MP without using any mercury. Firstly, the contact angle between the mercury and the substance surfaces is theoretically calculated by quantum chemical molecular dynamics. Secondly, a group of images showing the porous structure is obtained with an X-ray computed tomography scanner, and then a three-dimensional digital model is reconstructed connecting the pores/substances boundaries between each image. Thirdly, mercury intrusion which is a fundamental process of the MP method is digitally simulated. The digital mercury intrudes into pores of the digital model from its circumference with the theoretically calculated contact angle. Both the intruded volume and the corresponding pressure virtually applied to the digital mercury are simultaneously measured step by step. Finally, the pore size distribution as well as the porosity of each continuous and closed pore is obtained with the Washburn equation. As a result of the comparison of measured results between MP and DMP methods in applying to a porous material of diesel particulate filters, similarities such as the number of peaks, peak positions and spans in the pore size distributions have been found. Additionally, the porosity and the average pore diameter were 50.13% and 19.10 μm with DMP in comparison with 51.08% and 20.02 μm with MP, respectively.