The　dynamic　modeling　problem　for　flexible　two-wheel　upright　self-balance　humanoid　robot　is　researched　for　the　first　time.　A　dynamic　model　is　obtained.based　on　the　Lagange　equation　and　dynamics　mechanics　theory.　Using　spring　imitates　hominal　lumbar　spine　for　the　first　time.　Considering　the　lumbar　spine　of　flexible　robot,　which　has　an　actual　length　without　being　treated　as　an　approximate　point.　All　these　are　diffenent　from　previous　robots.　The　quality　of　upper　and　loiter　base　is　summetrical.　The　simplified　dynamic　model　is　obtained　by　design　and　its　structure　is　simple.　Controlling　is　easy　and　effective.　The　research　also　supplied　theoretic　instructions　for　developing　a　dynamic　control　system　with　flexible　two-wheel　upright　self-balance　humanoid　robot.　It　has　great　significance　to　design　and　research　for　humanoid　robot.