In　view　of　the　flexible　structure　feature　of　waist,　a　flexible　two-wheeled　mobile　robot　based　on　dynamics　of　flexible　multi-body　system　is　designed　in　this　paper.　Adopting　the　assumed　mode　method,　we　can　abstract　the　robot　to　a　three-link　robot　system,　and　establish　the　flexible　robot　dynamics　model　using　D＇　the　Alembert-Lagrange,　then　we　have　obtained　the　system　dynamics　equation　according　to　obliqueangles　of　the　three　poles　and　turn　corners　of　two　wheels　as　the　parameters,　and　the　system　vibration　equation　of　connecting　rod　with　waist　flexibility.　The　process　of　establishing　the　mathematics　model　is　provided,　and　the　simulation　analysis　of　the　model　is　conducted.　The　simulation　results　confirm　that　the　model　is　efficient,　and　it　provides　a　theory　basis　for　the　movement　and　the　control　research　of　the　flexible　robot.