First establish a dynamic model of tower crane in the load lifting process, the lifting load is solved.Then establish the FEM model of the tower crane under the normal and the damage condition. Get the dynamic displacement of the normal and the damage status under the lifting dynamic load. Propose a damaged diagnosis method by the displacement rate. The results of the study show that this method can not only diagnose the structural damage status, but also determine the positions of structural damage. This will be a new search on tower crane structural health diagnosis.