Turn is widely applied in the remote sensing test field, and the requirements for its control performance become increasingly high, especially for the control of low-speed, large -torque turn. To the problems that the classical state observer is unable to detect the system state precisely and it is hard to accurately describe the system model due to inaccurate estimation of rotational inertia and uncertain perturbation model, we proposed a control method based on Extended State Observer (ESO) to track the action of uncertainties, which is independent of the exact system model. Firstly, the ESO was analyzed and designed. Then, a nonlinear PID controller for speed loop was constructed, and simulation was made to the system under the Simulink. Results of the test show that the method can improve the performance of the control system of the low-speed, large-torque turn effectively. Compared with the traditional PID control, the accuracy of steady speed of the turn was improved by 8. 6%, and the tracking error was reduced by 13. 3%.