This paper establishes a three-dimensional (3D) finite element model based on continuum damage mechanics to simulate low-velocity impact on stiffener of a stiffened composite panel. In this model, the 3D Hashin criterion is employed to predict intra-laminar damage, while the cohesive zone model is utilized to predict inter-laminar damage. Numerical results show that for stiffener impact, once the contact force exceeds the threshold value, failure occurs in the stiffener web; afterwards, due to displacement discontinuity, mode II crack propagation initiates at the stiffener/skin interface, resulting in extensive debonding. The numerical simulation results show good agreement with experimental data reported in the literature, demonstrating that the proposed model can well predict stiffener impact damage of the stiffened composite panel.