Filling grouting material into the voids of porous asphalt mixture (PAM) is one of the important steps in the construction of pouring semi-flexible pavement (SFP), and the pore characteristics play a dominant role in the slurry permeability performance of PAM. Therefore, understanding the influence of pore characteristics on the slurry permeability performance and revealing the penetration mechanism of grouting materials in the void of PAM are essential for guiding the design of PAM used in SFP and improving the quality and efficiency of the grouting construction. Firstly, the effects of porosity and aggregate size on slurry permeability and water permeability of PAM are experimentally studied. Then, the 3D pore structure parameters, such as porosity, equivalent diameter, coordination number, pore throat dimension and tortuosity are quantitatively and statistically analyzed via X-ray CT and 3D reconstructed model. Finally, the slurry permeability simulation of PAM is conducted. The results show that the porosity and aggregate size have a significant influence on the complexity and spatial anisotropy of the pore structure of PAM. Increasing the porosity and aggregate size can effectively increase the connected porosity ratio, 3D pore size and throat size of PAM, while reduce the number of small pores (D-3d < 1 mm(2)) and isolated pores. Besides, the slurry and water permeability coefficients of PAM are also positively correlated with the porosity and aggregate size. Moreover, to be consistent with the real condition, the slurry permeability coefficient is more suggested as the technical index of PAM to ensure the perfusion effect of PAM. In the simulation, the slurry permeability values in the vertical direction are higher than those in the horizontal direction. The pore characteristics are ranked according to their effect on the seepage of grouting material: connected porosity > pore size and throat size >> pore coordination number (CN) and tortuosity.