Abstract: To investigate the influence of joints on uniaxial compression behavior of jointed coal,the synthetic coal mass specimen was first constructed based on the in-situ measurement of joints and numerical parameters calibration tests. Then the numerical uniaxial compression tests on intact coal and jointed coal with REV size under different load-ing orientations were conducted. Finally,the influence mechanism of joints on the mechanical behavior of jointed coal and the fracture formation mechanism were analyzed. The study shows that:① The constructed synthetic coal mass model can represent the jointed coal investigated,with the REV equaling to 1. 0 m×1. 0 m×2. 0 m. ② Joints weaken the UCS and elastic modulus,but increase the deformation of jointed coal under uniaxial compression,with the weake-ning / increasing degree depending on the relation between loading orientations and joints. ③ Joints determine the fail-ure mode of jointed coal under uniaxial compression. The jointed coal by splitting fracture parallel to loading directions,with different splitting geometries under different loading orientations. ④ The contribution ratio of matrix failure and the contribution ratio of joints activation were put forward,which can be used to quantitatively evaluate the contri-bution degree of matrix failure and joints activation to the failure of jointed rock,respectively. ⑤ The joint parallel to loading orientation is converted to activated pre-existing fracture under the effect of loading force,from the end of which grow the wing crack,both of which form the compression-induced tension fracture composition. For jointed coal containing non-penetrating joints,the splitting fractures are formed by the coalescence of fracture compositions. For the coal mass containing through joints,the splitting fractures are formed only by the through activated pre-existing frac-tures.