Abstract: The measure of deformation, failure and damage of geotechnical materials concerns the reliability of calculation results. Considering the incompleteness of damage model, it is proposed that the ratio of strain deviation of the linear elastic strain to strain could be used as the damage value. The analysis and calculation results of experiment indicate that the method can calculate preciously the initial and limit damage. On the same time, on the basis of brittle failure test of rocks, it is pointed out that there exists an interval of sudden increase of damage in transition from elastic stage to non-elastic stage of materials, which is related to the extension and mutual blinding of micro-cracks in rock materials. In this interval the strain and damage in rocks may be locally concentrated.