The friction nonlinearity in the servo system of an air-borne opto-electronic tracking platform causes creeping phenomena in the lower velocity and increases the steady error of the servo system. It is difficult for the routine PID controller to satisfy performance specifications of the high precision servo system of the opto-electronic tracking platform. An Active Disturbance Rejection Controller (ADRC) with a new control function of the second-order discrete system is studied. The new ADRC is used as the position-loop controller in the servo system of the air-borne opto-electronic tracking platform. The experimental results show that the position tracking error of the servo system is less than ±(4.1×10-3)° and the velocity tracking error is less than ±0.024°/s after 0.5 second when the servo system tracks the sine input signal whose amplitude is 0.5° and frequency is 0.159 Hz. They demonstrate that the ADRC increases the position and the velocity tracking precision of the servo system through effective compensating the friction nonlinearity.