Considering that disturbances rejection is the main problem of control design of two-wheeled self-balancing robot system, this paper proposes a double-loop control scheme based on ADRC to implement stable upright control of the robot. In this scheme, a PID control algorithm is employed as inner-loop controller to execute speed closed-loop of the motor, and the ADRC technique is applied to design the pitch angle controller of the robot where an optimized parameter design of ESO is used to improve the controller performance. Extensive simulation and experiment results show that the proposed control shceme, compared with the traditional double-loop PID control, is with stronger robustness to the load change and external disturbance.