Abstract: Identification of weak links in machine tool structural rigidity is a key link to improving machine tool machining performance. In this paper, the machine tool structure was equivalent to a cantilever beam structure, and the static stiffness of the cantilever beam was studied by dynamic testing. Based on this, a method was proposed to identify the weak link of cantilever beam stiffness by using curve corner index. The MATLAB finite element model of cantilever beam was taken as a numerical example, and the dynamic data of each node of the numerical model was obtained by using the state space method. After Fourier transform, the amplitude at 0 Hz was extracted to construct the corner index. The weakening of the elastic modulus of the element was used to simulate the weak link of the stiffness. The evaluation effect of the corner index under the three conditions of single element stiffness weakening, two element stiffness weakening, three element stiffness weakening and noise participation was studied respectively. The numerical simulation and experimental research show that the curve corner can be used to better evaluate the weak link of cantilever beam and has certain practical engineering value.