Damage of a sampling fused silica reflector has been observed when the performance of the 9th beam of Shenguang-Ⅱ was tested. By analyzing the inducement and mechanism,it is confirmed that the transverse stimulated Brillouin scattering (TSBS) induces the damage.Increasing the bandwidth by 30 GHz can prevent further damage efficiently.A propagation model of TSBS in large aperture fused silica has been established,which can calculate the intensity threshold of laser induced damage in fused silica. Theoretical calculation and experimental results show that the fused silica glass will be damaged if the energy of large aperture(310 mm diameter) narrow bandwidth laser reaches 2～3 kJ.