The carrying capacity decreases continuously as the material property deteriorates under the action of some external factors. It is important to evaluate the damage of concrete, in which the damage parameter plays an important role. An experimentation method is designed in this paper, with which we can simulate the initial damage by mixing initiator into concrete. Using the elastic modulus of axial tension experimentation, the tension initial damage D0 and tension damage Peak value Df have been gained. The Size effect of concrete tension damage parameters is verified. The curve of damage-parameters and size is gained, the trend of the tension damage parameters is obtained.