Fracture behavior of biological porous dentine is important to the success of dental restoration. The role of peritubular dentine (PTD) microstructure on the fracture properties of human dentine is investigated by analysis of its crack tip shielding effect on microcracks and macrocracks. The evolution of microcracks around the dentine tubules (DTs) and the growth of macrocracks in the dentine are experimentally observed by scanning electron microscope. Two cases of an individual PTD&DT penetrating the microcrack tip and locating ahead of the microcrack tip are discussed. The effects of multiple PTD&DTs with random distribution and various porosities on the macrocrack shielding or amplifying in dentine are also particularly investigated. The importance of modulus, thickness of PTD and porosity of DT to the shielding effect of crack growth in dentine is studied by finite element analysis, which is characterized by the dominated fracture parameter J-integral. Numerical results demonstrate that PTD can shield the growth of dentine microcracks. When the PTD is in a specific location around macrocracks, it also has a shielding effect. The thicker and harder the PTD, the greater the shielding effect on crack growth. In conclusion, the porous dentine can be used as a reference structure in the design of implant dentures to enhance the dentine toughness.