This paper present a method for the assesment of vibration fatigues in engine exhaust system. Analysis technologies by virtual model can reduce the no. of physical tests and development cycles. The prediction processes are based on the construction of FE model for the exhaust system, normal mode analysis and frequency response analysis. The analysis results of eigen frequencies are compared with the model test results. And frequency response results of accelerations and stresses at critical locations were also presented. The analysis method could be applied to asses the vibration fatigue for the engine exhaust manifold. It shows a good agreement between numerical and experimental results.