Abstract: The relationship between the failure of the tunnel and initial stress field is known by the method where the failure processing in different initial stress fields is simulated by using RFPA2D developed by Northeastern University.According to the simulation result，in the condition of vertical stress greater than horizontal stress，the failure occurs in lateral wall of the tunnel.On the other hand，the failure occurs in the roof and bottom.The greater the ratio between two stresses is，the stronger such trend is.The failure simultaneously occurs in the roof，lateral wall and bottom when the vertical stress is same with the horizontal.In other word，the failure type of tunnel is in connection with the ratio of two stresses and not related to the level of stress.

Key words: RFPA2D, Numerical simulation, Stress field, Stability, Tunnel