38%和57%。 The FEA model of a semi-trailer frame was established by taking plate as a basic element. In order to find out the reasons of the frame abnormal rupture, both static analysis and modal analysis were carried out by using the NASTRAN FEAS software. The results of FEA showed that the rivet which connected the forth cross rail and side rail and the first rivet in front of the side wing plate had high alternate stress and stress value which was higher than or close to the yield strength of the material. The calculation results gave the causes of the frame abnormal rupture and accorded with those of the frame abnormal rupture in practice, which verified that the finite element model and analysis method were practical. According to the requirements of real process, the way for the reconstruction of the frame structure was also given, which was proved effective by the reconstruction results. The strength of the rupture parts was higher than the original and the maximal stress value decreased 38% and 57% in bending case and twisting case respectively.