In this paper, to stabilize the quadrotor unmanned aerial vehicles (QUAV) with suspended load against external disturbances and uncertain parameters, the sliding mode control (SMC) is utilized to control the QUAV follow the desired trajectory, while the extended states observer (ESO) is used to estimate states of the plant and disturbances for the position and altitude control loops. The dynamic model of the QUAV is established based on Euler angles under the influence of aerodynamic moments and force. To control the UAV along the reference trajectory, a controller with two loops is utilized: an outer loop is position control loop, and an inner loop is control-altitude loop. Both of them are designed utilizing SMC with ESO to ensure the sustainability of the controller under disturbances. These disturbances are environmental external forces, the effect of slung payload, and uncertain model parameters. Finally, Matlab/Simulink is used to verify effectiveness and feasibility of the proposed SMC-ESO control system for QUAV.