As the research object of this paper, the self-balancing unicycle robot system has some typical characteristics such as multivariable, high order and nonlinearity. In view of the self-balancing unicycle robot system's characteristics, the author built a mathematical model of the system and designed a LQR controller for the self-balancing unicycle robot. Moreover, simulation and experiment are presented to test and verify the effectiveness of the LQR controller. The experiment results indicate that the LQR-based control system of self-balancing unicycle robot has faster response speed, higher stability and better robust stability. And it's very easy to apply the method into practical application.