Abstract: The presence of discontinuities and randomly distributed pores in basalt specimens greatly affects their engineering properties, such as the failure mechanism and strength. Therefore, investigating the mechanical and fracture behaviors of basalt affected by the pre-existing defects is important for underground engineering, mining engineering, foundation engineering, and rock breaking and blasting. Laboratory tests have been widely used to research the failure mechanism of rocks under different conditions. However, it is difficult to clearly show the internal or spatial crack evolution during rock failure process in laboratory tests. Recently, X-ray computerized tomography (CT) and numerical tests have been used to detect the internal microstructures of rock specimens and to study their failure mechanism and strength. In addition, tensile strength is an important mechanical property of rock material. The direct tensile test is theoretically the simplest and most effective method for understanding the tensile behavior of rock. However, it is difficult to carry out in practical condition, because the sample processing and test procedures are complicated, also the experimental process of each sample cannot be repeated and has limited results. Due to the opacity of rocks, it is difficult to examine the three-dimensional internal structures of rocks through traditional physical and numerical experiments. In the present research, a 3D numerical method was proposed for simulating porous rock failure based on CT technology, the edge detection algorithm, filtering algorithm, and 3D matrix mapping method. Direct tensile tests were carried out based on the parallel finite element method to study the effect of the porosity and pore distribution on the failure mechanism and tensile strength. The results indicate that initial cracks at the beginning of loading usually occur in pores, and then with the raising of load the initial cracks propagate along the direction perpendicular to the loading direction and eventually form macroscopic tensile cracks. The porosity and pore distribution have significant influences on the position of macroscopic tensile cracks. The acoustic emission (AE) event numbers and the accumulative AE energy are gradually decreased as the porosity increased. In addition, the brittle failure primarily determines the tensile failure mode and the presence of pores weakens the tensile strength of basalt samples.