Abstract: Najar energy method defines damage dissipation energy and nondestructive strain energy, and the ratio of those two is defined as the damage variable. The principle of the method is clear, but the method can't well describe the actual process of concrete uniaxial compression failure. In this paper, this method is improved, the delamination of elastic deformation and plastic deformation in the process of concrete compressiona is done, and a new damage variable is defined. In order to make a comparison between those two methods, the uniaxial compression tests of concrete under different loading rates are carried out, and the experimental data are fitted. Based on the fitted data, the damage variables in the compression process of concrete are calculated by those two methods, and the relationship curves between the damage variables and strain are obtained from the experimental studies. It is found from the experimental studies that the improved Najar energy method is more simple and more convenient than the conventinoal methods, and it is also more conformable to the general failure law of concrete under the uniaxial compression. At the same time, the relationship curves also reflect the strain rate effects of concrete.