In nature, some flaws (such as fissures, joints, weak surfaces, and faults, etc.) are pre‐existed in the rock masses, which have been proved an important influence on the mechanical properties of rock masses. In this paper, a three‐dimensional (3D) joint model of a fractured specimen is built by means of the computed tomography (CT) scanning technic and digital image processing. The model shows three joints exist in the specimen: an essential joint which can be found from the specimen surface and two extra‐essential joints can only be detected from the 3D joint model. The 3D joint model is integrated into 3D particle flow code (PFC3D) to build a jointed numerical specimen and triaxial compression tests under different confining pressures are simulated. The results show that the linear phase of the stress‐strain curve is more significant under larger confining pressure. The peak strength of the jointed specimen increases linearly with the confining pressure. In addition, the peak strength of the jointed specimen shows highly consistency with the residual strength of the corresponding intact specimen. For both the intact and jointed specimen, Young's modulus increases nonlinearly with the confining pressure, and remains constant after confining pressure reaching 20 MPa.