There are input constraints and uncertainties in the control of coaxial multi-rotor UAVs.To solve the problems,a robust UAV control method based on the adaptive observer is proposed.Firstly,the mathematical models of position and attitude of a coaxial 12-rotor UAV with uncertainties are established.In the design of robust control law of the position loop,an auxiliary observer is introduced to compensate for the effect of input constraints.Then,in the design of robust control law of the attitude loop,an adaptive observer is introduced to suppress the effect of uncertainties.These methods help realize global asymptotic stability of the coaxial multi-rotor UAV.Simulation results show that the proposed robust control law has better stability, accuracy and rapidity,and can realize the robust control of coaxial multi-rotor UAVs within a shorter time with the maximum error in position and attitude tracking of only 0.05 m and 0.2° respectively.