Aiming　to　the　flexible　structure　feature　of　waist,　the　flexible　two-wheeled　mobile　robot　was　designed　based　on　dynamics　of　flexible　multi-body　system.　Adopting　the　assumed　mode　method,　the　robot　can　be　abstracted　to　a　three-link　robot　system,　and　the　flexible　robot　dynamics　model　is　established　using　D＇　the　Alembert-Lagrange,　then　the　dynamics　equation　of　this　systems　is　obtained　using　the　oblique　angles　of　three　poles　and　the　turn　corners　of　two　wheels　as　the　parameters,　and　the　vibration　equation　of　connecting　rod　with　flexible　waist　is　also　gained.　Listing　some　material　steps　at　establishing　the　mathematics　model,　and　from　this　some　simulation　analysis　was　carried　out.　The　simulation　results　confirm　that　the　model　is　efficient,　and　it　has　provided　the　theory　basis　for　the　movement　and　control　research　of　the　flexible　robot　system.　©　2008　Springer　Berlin　Heidelberg.