Abstract: The dynamic modeling problem for the flexible two-wheel upright self-balance humanoid robot is tackled.A dynamic model for the flexible two-wheel self-balance humanoid robot is obtained based on Lagrange equation and dynamics theory.Spring is used to imitate hominine lumbar spine and flexible lumbar curvature of the robot is considered,which are different from previous robots.The gained dynamics model is linearized and its state-space equations are established.The structure of the established dynamic model is very simple,and it is easy to control the robot effectively.Simulation results prove the system stability,and experiment results are analyzed in detail,verifying that the system modeling and the linearquadraic regulator(LQR) controller design are valid and rational.