A sliding mode control algorithm based on extended state observer(SMC-ESO) is proposed to solve the problem of tracking accuracy decrease due to the external environment of ship borne space optical communication and the influence of nonlinear model uncertainty inside the turntable. This algorithm uses the extended state observer to observe and estimate the internal disturbance of the turntable caused by the nonlinear disturbance moment and the external disturbance caused by the ship's swing, and takes the estimated disturbance value as the compensation of the sliding mode controller, so as to eliminate the influence of the disturbance on the controller and improve the control performance of the sliding mode controller. The simulation results of transmission mechanism show that the proposed SMC-ESO algorithm can improve the disturbance rejection performance by 44.22% compared with the proportional integral differential(PID) algorithm, and can meet the control requirements of coarse tracking application.