A cascade controller architecture is designed to realize the attitude control of quadrotor with unknown disturbances in this article. The cascade controller integrates the advantages of the triple-step method and a nonlinear integral sliding mode. In the inner loop, an extended high-gain observer is designed to estimate total disturbance, including model uncertainty and external wind disturbance, in real time. Moreover, a nonlinear integral sliding mode with the capability of small error amplification and large error saturation is introduced to compensate for the estimated disturbance and track desired angular velocity. In the outer loop, a TD-based triple-step controller is designed to guarantee fast tracking of attitude angle. The convergence of tracking errors of both inner and outer loops is proved through the Lyapunov theory. Finally, both simulation and experimental results demonstrate the effectiveness of the proposed control method.