A two-wheeled coaxial inverted pendulum system was derived using the wheel motor torques as inputs and taking the nonholonomic no-slip constraints into account by Lagrange method. The purpose was to make the mobile inverted pendulum move at the reference translational speed and rotational speed in the twodimensional plane while keeping its link balanced. The statespace function of the closedloop system was established through state feedback, and the input was deduced from the pole placement. The simulation result shows the validity of the system's state equation and the reasonableness of the control method.