This paper introduces a method for calculation of dynamic stress occurring in flexible bodies of a moving multibody system by using commercial softwares DADS for dynamic analysis and MSC/NASTRAN for finite element analysis. Three methods for model transient response analysis of a flexible body are summarized. Elastic deformation of a flexible body can be described with normal modes and static modes composed of constraint modes and residual attachment modes. The deformation modes divided into fixed-interface modes and free-interface modes can be determined by using MSC/NASTRAN and selected for dynamic analysis. The dynamic results obtained from DADS are utilized to calculate dynamic stress by using mode-displacement method or mode-acceleration method of MSC/NASTRAN. As a numerical example of the analysis, we used a three dimensional slider-crank model with a flexible connecting rod.