Abstract: In order to research the failure mechanism of bond between ribbed bars and concrete and discuss the influence of rib outline on bond behavior at a meso-level, a 3-D mesoscopic numerical model for reinforced concrete was established with ANSYS parametric design language. This model is based on a mesoscopic model for concrete and considers bars, and elements of each mesoscopic phase are generated by refining interface elements and distinguishing material properties. Two numerical models for pullout specimens for crescent-ribbed bar or screw thread bar were established respectively, and their bond failure processes were simulated. The damage and fracture region of concrete and the stress state of ribs were analyzed. The results show that the bond strength between a crescent-ribbed bar and concrete is slightly lower than that between a screw thread bar and concrete, but the stress concentration in concrete between crescent-ribbed bar's ribs is low and the damage degree is light. The simulated bond stress and bar slippage are approximate to their experimental values to show that the proposed numerical model can be used to research on bond behavior between bars and concrete.