Abstract: In order to realize the in-situ evaluation of concrete bridges subjected to fatigue for a long time, an evaluation method for cumulative damage of concrete structures is proposed, based on unloading elastic modulus. First, the value of elastic modulus is discussed by the definition of damage mechanics and the concrete initial condition is suggested using the static elastic modulus. Then, according to the concrete stress-strain curve and the statistical relationship between residual strain and cumulative strain, the calculation method of static equivalent strain and residual strain concrete are proposed by unloading elastic modulus and the method for estimating the strength of concrete after damage. The detailed steps of field test and analysis and the phase characteristic value of elastic modulus ratio and residual strain are developed. Based on the above research, the indicator of residual strain is compared with the indicators of modulus of deformation and static equivalent strain to indicate the most effective for damage evaluation of concrete. Therefore, the concrete damage degree is divided into four grades by the practical limiting value of residual strain. Finally, according to the measured concrete strength and elastic modulus ratio, a look-up table assessment method is put forward to evaluate the concrete residual strength and damage degree so as to simplify the evaluation process and it can be used as a practical evaluated method for cumulative damage of concrete.