Rockburst process of the surrounding rock of a circular tunnel is modeled by use of FLAC.Effects of the horizontal stress that is less than the vertical stress and the post-peak brittleness of rock are studied.The rock elements exhibit linear strain-softening behavior after the occurrence of failure and ideal plastic behavior and the failure meets the composite Mohr-Coulomb criterion with tension cut-off.The tangential stress of a row of elements in the surrounding rock is monitored.The tangential stress rock-burst criterion proposed by Xu and Wang is used to determine the state of elements.Numerical results show that the angle between the line（linking the V-shaped notch tip and the central point of the tunnel） and the horizontal axis of the tunnel increases to 45°from that less than 45°as the horizontal stress is increased. As the horizontal stress increases

the number of the failed elements and the elements occurring rockburst increases and the peak tangential stress is increased.At higher post-peak brittleness of rock

the shear bands become apparent

and it is easy to form the V-shaped notches.The number of the failed elements and the elements occurring rockburst increases.The distance between the rock with peak tangential stress and the tunnel surface is increased.