To solve the trajectory tracking problem for quadrotor unmanned aerial vehicles with immeasurable velocity and control input saturation, a dynamic surface output feedback control scheme is proposed in the presence of model uncertainties and unknown external disturbances. Firstly, the nonlinear extended state observer is designed to estimate velocity information and generalized perturbation term of the system. Then a no velty dynamic surface controller is designed based on the backstepping method with the dynamic surface technique, which can reduce the complexity of the control algorithm. Furthermore, the hyperbolic tangent function and a constructed aid system are introduced to process the control input saturation problem. Finally, by using Lyapunov analysis, it is proven that all signals of the closedloop trajectory tracking system are the uniformly ultimate boundedness under the proposed control strategy. The simulation results on DJI M100 aircraft model show that the output feedback controller can effectively deal with the control input constraints, velocity immeasurability and unknown disturbances of quadrotor system, and realize the task of trajectory tracking control accurately.