Abstract: Because the precise control of quadrotor requires the thrust produced by propulsion system, and the thrust is hard to be measured directly on quadrotor. A hovering thrust estimation method was proposed for the quadrotor to solve the problem. Modeling a propulsion system of quadrotor, a linear system was established for thrust estimation in hovering state, and the input of propulsion system, attitude and altitude measurement of quadrotor were taken as the input of the new linear system, and thrust of quadrotor was estimated by using state observer.The results show that, this thrust estimation method based on propulsion system model can effectively estimate the thrust generated by quadrotor propulsion system in hovering.