Aimed at the problems that nonlinear systems are confronted with uncertain dynamics, unknown external disturbances and input constrains, an asymptotic tracking controller considering input saturation is proposed. Firstly, the uncertain dynamics and external disturbances in the system are integrated into the bounded "total disturbance term". Then, the control law and the adaptive law are designed to compensate the disturbance term to make the tracking error asymptotically converge to zero rather than just a bounded compact set. Compared with the traditional control method of nonlinear systems considering uncertain dynamics and external disturbance, the proposed controller is simpler in structure and the proposed method is good in precision. In addition, by designing an auxiliary error compensation system, the controller can cope with the input saturation situation well, and the compensation signal can converge to zero asymptotically after the saturation condition is removed. Finally, the proposed method is valid.