Abstract: In order to investigate the change of vibrating state of vibrating screen’s girder before and after appearance of cracks on the girder, ABAQUS-based finite element analysis on modality and forced vibration state is made with the girder of the AHS3661 vibrating screen as the object study. Analysis shows that in the absence of cracks, the simulated maximum stress of forced vibration of the girder is 89 MPa with a maximum displacement approaching 10 mm, which are consistent with the actually measured values and testify the validity of the F-E analysis in this regard; with the appearance on the girder near the exciter of a 5 mm-deep crack without penetrating through the steel plate, the displacement of the girder under forced vibration reaches 19.5 mm with the maximum stress appearing at the cracking point with a magnitude of 201 MPa; in the presence of a 10 mm crack near the exciter, which extents through the steel plate, the maximum displacement of the girder under forced vibration reaches 93.4 mm with the maximum stress going up to 577 MPa; in the case that a 5 mm crack appears in the middle section of the girder, the girder tends to vibrate with a maximum amplitude of 18.3 mm and a maximum stress of 291 MPa at the cracking point; and at the time when there appears in the middle section of the girder a 10 mm crack which extends through the steel, the girder is seen to vibrate with a maximum amplitude of 27.8 mm, and a maximum stress of 482 MPa at the cracking point. Viewed as a whole, cracking of the girder would cause the girder to undergo changes in vibration mode and to vibrate with increased natural frequency and amplitude, causing as a result the stress near the cracking point to be noticeably higher than those in other areas. The work in the paper may serve as a theoretical basis for making fault diagnosis on site and adoption of preventive maintenance measures.