To study on non-uniform stiffness degradation in structure caused by adverse environmental effects and damage, an identification method for stiffness degradation is proposed based on the change rate of frequency using bending beam model, which considers the variation of modal deflection curvature and natural frequency before and after damage. Firstly, modal deflection curvature is derived through a flexibility matrix, and the damage area and location are determined through the variation of modal deflection curvature before and after damage. Then, the damage area is divided into segments, after that the matrix function of damage extent, location parameters of damage area and natural frequency is established according to the vibration theory of Euler-Bernoulli beam. It can directly assess the damage degree of different segments through the change rate of frequency. The results show that the method can precisely identify the location and extent of the local damage, and has advantages in assessment of the non-uniform stiffness degradation in structure.