Ceramic-glass is an important material for large space telescopes (LST) and laser gyroscope. But during the ultra precision machining process, surface damages may exist inside the workpiece, which greatly decreases the optical performance of ceramic-glass. Indentation method is utilized to research the critical condition of crack brittle-ductile transition of the ceramic-glass. Based on this, the influences of brittle-ductile transition affected by processing fatigue are investigated by the cycle nano-indentation test, as well as the variation pattern of the glass′s critical pressure under the fatigue condition and the influences of critical grinding depth caused by fatigue factors. Results show that, the grinding cycle process causes the workpiece′s surface accumulating mechanical damage, which leads the decreased fracture toughness of the ceramic-glass material and it′s plastic domain. Results also shows that it is the cycle index that connected with the critical pressure load which cracks the surface of the ceramic-glass: the more the cycle times, the lower the critical pressure load. Besides, the critical grinding conditions of the brittle-ductile transition are determined. Research results provde a certain reference to the improvenent of the optical element surface quality.