Abstract: The soil density is a key factor for the studies on the limit support pressure and the face stability operation during tunneling construction. Based on the Kirsch’s laboratory model tests, the PFC^2D is employed to investigate the influence of soil density on the limit support pressure, residual support pressure and void ratio in the heading face. The failure mechanisms of the excavation face are investigated at the mesoscopic level. The failure behavior and arrange of the face stability of the shield tunnels in sand are analyzed. The improved wedge model is proposed as a method for calculating the limit support pressure of face. It may provide certain guidance to the stabilization of excavation face of shield tunnels.