Aiming at the attitude control problem of quad-rotor aircraft with modeling uncertainties and external disturbances, an observer based adaptive sliding mode control algorithm is proposed. Based on the establishment of attitude error dynamics model of quad-rotor aircraft, the unknown state feedback of the system is obtained by the global asymptotic convergence observer, the adaptive sliding mode control is used to suppress the uncertainty and interference of the system. Finally, an adaptive sliding mode attitude, controller based on observer is constructed.The stability analysis based on Lyapunov shows that the tracking error of the method is uniform and ultimately bounded. The results of numerical simulation show that, compared with the existing sliding mode control method, the proposed method has better attitude tracking performance and higher anti-disturbance robustness. It can effectively guarantee the attitude tracking control performance of the aircraft with higher robustness.