Abstract: Three-dimensional internal crack is an inherent property of brittle materials such as rocks, which has a great influence on the fracture failure characteristics of materials.Most of the previous researches focused on surface cracks or penetrating cracks that could be simplified into two-dimensional problems.There are few studies on three dimensional internal crack interactions.Based on 3D-ILC,internal cracks were generated without damaging the sample surface.Then we carried out uniaxial tensile test for samples with and without impedimental crack.The stress distribution was observed qualitatively by means of the stress birefringence effect, and the numerical simulation was carried out at the same time.The results show that:① Internal cracks made by 3D-ILC can penetrate through each other, which lays a foundation for solving the problems of the fusion and penetration three-dimensional internal cracks in fracture mechanics.② The vertical impedimental crack destroys the stress distribution of the double coplanar crack, which can reduce the stress concentration of tips near the impedimental crack.③ The vertical impedimental crack can promote the crack initiation of samples, which cause the initiation load on the inner side of the coplanar crack decreased by 10% and the initiation load of lateral tip of coplanar crack decreased by 2.5%,the failure load decreased by 26.1%.The crack initiation load of the sample with the impedimental crack is 33.7% of the failure load, and the crack initiation load of the sample without the impedimental crack is 41% of the failure load.④ The impedimental crack does not change the fracture mode of the samples.Both samples show pure I type failure characteristics, and form smooth fracture surfaces along the plane where the double coplanar cracks are located.⑤ The impedimental crack will enhance the stress release during the fracture of the sample, and generate a large amount of residual stress around the impedimental crack.⑥ According to the maximum tensile stress criterion(MTS),the samples were simulated numerically, and we obtained the propagation process of cracks, the final failure pattern and the distribution rule of stress intensity factor at the crack tip, which was consistent with the test results.