According to the system of twowheeled selfbalanced robot, a nonfragile controller is designed via linear matrix inequality (LMI) method in this thesis. Then, by using matrix inequality converter technique and Lyapunov function method, the sufficient condition of controller that based on observer is obtained via linear matrix inequality (LMI) method. Comparing with the existing research method of controller, the problem of nonfragile that controller has uncertainties are consider in this paper. The designed controller can meet the system stability with the uncertain perturbation. Finally, the MATLAB simulation experiment shows the validity of the proposed method.