The　dynamic　modeling　problems　of　flexible　two-wheel　upright　self-balance　humanoid　robot　are　researched.　A　dynamic　modeling　is　obtained　by　the　Lagrange　equation　and　dynamics　mechanics　theory.　Using　springs　imitate　human　lumbar　spine,　considering　the　lumbar　spine　of　the　flexible　robot,　which　has　an　actual　length　without　being　treated　as　an　approximate　point.　All　these　are　different　from　previous　robots.　The　quality　of　upper　and　lower　base　is　cancelled.　The　dynamic　model　is　linearized　and　its　spatial　equations　of　state　are　established.　The　simplified　dynamic　model　is　obtained　by　designing　its　structure　in　simple　ways,　in　this　way.　It　is　convenient　to　control　the　robot.　The　state　feedback　controller(LQR)　with　good　robustness　is　designed　on　Matlab.　The　stability　of　systems　is　proved　by　the　experimental　results.　Validity　and　rationality　of　the　system　modeling　and　the　controller　designing　are　verified　through　the　performance　experiments　of　the　prototype.　The　research　also　supplies　theoretical　instructions　for　developing　the　dynamic　control　system　in　the　flexible　two-wheel　upright　self-balance　humanoid　robot.　It　has　great　significance　in　design　and　research　for　the　humanoid　robots.　©　2008　Springer　Berlin　Heidelberg.