In this paper, modal strain energy-based approach is developed for damage detection in plate-like structures. In order to overcome the limitation of measuring points, a central difference method is newly employed to compute the partial differential terms in strain energy formula. Finite element analysis is conducted on an aluminum thin plate to obtain the mode shapes before and after the occurrence of damage. Feasibility of the proposed approach is proved by investigating three plates with different types of boundary condition. A damage index is presented to identify the location and extent of crack in the plate-like structures. The analytical results show that the proposed approach accurately identifies the crack in the plate structure with various types of boundary condition by using appropriate mode shapes and damage threshold.