This paper is major talking about critical speeds and modes ofrotor-bearing system. We use Galerkin's method to find the equation ofmotion. The computer is very advanced and fast now. If we producevirtual prototypes in computer, and do the analysis and optimum designin computer. It can reduce many time and money to compare withproducing physical prototype. In this paper, we do the simulation offlexible overhang rotor in mechanical system simulation softwareADAMS, and to compare the result with the numerical solution.