The structure of active disturbance rejection control(ADRC) technique is described in detail, including the tracking differentiator, extended state observer and nonlinear state error feedback. Typical algorithms of each part are given as well. In order to control the attitude of a quadrotor hovering system as we desired, we design three kinds of discrete ADRC. Simulations and real time control experiments are carried out based on Simulink. After parameter adjustment,experimental results can be obtained and ...