The relationship between spall strength and impact stress of AD95 ceramics which is in a one-dimensional strain state is determined by velocity profile measurement of the free surface or the sample/window interface. All fiber displacement interferometer system for any reflector is used in velocity measurement. Further the relationship between shock compressive damage degree and impact stress is discussed. The results indicate that the stress threshold of AD95 ceramics against shock compressive damage is about 3.7 GPa, which is less than its Hugoniot Elastic Limit (HEL, about 5.47 GPa). When impact stress is less than the threshold, no compressive damage occurs, and the spall strength increases with impact stress gradually. When impact stress is greater than the threshold, shock compressive damage occurs and develops rapidly which leads to the decrease of the spall strength with impact stress. The spall strength falls to zero when the impact stress increases up to about the HEL, which indicates that the material has lost the ability to resist the tensile stress and severe shock compressive damage has happened.