Growth of laser induced damage on the surface of fused silica plays a major role in determining optics lifetime in high power laser systems. CO2 laser is used to mitigate the damaged spot. It locally meltes and evaporates the fused silica surface, producing smooth, Gaussian shaped pit, eliminating the cracks and rough, uneven on surface. Moreover, the damage threshold of mitigation spot is much higher than the damage growth threshold of fused silica. So CO2 laser mitigation treatment can successfully inhibit the growth of laser-induced surface damage on fused silica. The temperature distribution on the surface of fused silica induced by a CO2 Gaussian beam has been discussed to analyze the formative process of Gaussian shaped pits and determine the best mitigation parameter. Atomic force microscopy (AFM) and profiler are applied to observe the micro-structure of damage and mitigation spots. Finite-difference time-domain (FDTD) method is applied to calculate the light intensity distribution around the mitigation and damage spots. They provide useful information to understand the mitigation mechanisms.