Abstract: A numerical model of rock ring disk was constructed using two-dimensional particle flow code frame. The influence of the inner-outer diameter ratio \eta of the rock ring disk on the response of stress-strain curves, microcracking evolution behavior and failure mode were analyzed. Simulation results show: (1)The stress-strain curve changes from a typical unimodal form to a form with flat interval with the increase of the diameter ratio \eta. (2) The tensile strength of the ring disk decreases exponentially with the increase of the diameter ratio \eta.(3) The failure mode evolves from radial splitting to four-fan-shaped failure mode with the increase of inner-outer diameter ratio \eta. (4) All numerical results are in good agreement with the experimental results. The simulation results can provide reference for the researchers to understand the failure mechanism of ring samples.