| The pressure arch of tunnel was a key problem in tunnel engineering，the continuous medium numerical simulation method was lacking in microscopic study of tunnel pressure arch characteristics，and the discrete element method which was good at microscopic study required large computer storage space and long calculation time. Based on the existing discrete-continuous coupling model, the continuous model boundary which was in contact with dispersed particle was regarded as the wall in PFC2D. Coupling relationship between discrete model and continuous model was achieved through the transmission of force. Calculation method of mean stress, calculation area of mean stress and traversal particle method of coupling procedure were studied. The stress characteristics of surrounding rock after tunnel excavation ，the formation mechanism of tunnel pressure arch and the tunnel pressure arch characteristics were studied based on the self-developed and optimized discrete-continuous coupling model. The equivalent area of stress concentration of tunnel pressure arch generated by tunnel excavation were calculated under the different buried depths of 10, 14, 18, 22, 26, 30, 34m, which was revealing the variation law of tunnel pressure arch with tunnel buried depth. The results show that，the self-developed and optimized discrete-continuous coupling model can not only ensure the calculation accuracy, but also give full play to the advantages of discrete element method in microscopic study. Layered pressure rings appear near the excavation face after tunnel excavation, and the indirect contact force between the layered pressure rings of vault and invert bottom reduces, the bearing capacity of surrounding rock decreases. The equivalent area of stress concentration of tunnel pressure arch is decreasing with the increase of tunnel buried depth，and the bearing capacity of tunnel pressure arch is increasing. However, tunnel pressure arch is stability when the tunnel depth reaches a certain limit.