A novel attitude tracking controller is proposed for the 3-DOF helicopter under input and output constraints. A barrier Lyapunov function is employed to address input constraint, and an auxiliary design system for output constraint. Combining the backstepping technique, a nonlinear disturbance observer is explored to tackle the unknown nonlinear functions. We proved that the presented method can control the system output errors converge to a neighbourhood of zero for any sufficient smooth and bounded time-varying trajectory, and simultaneously the input and output states remains in the prescribed set uniformly. Simulation results demonstrate the effectiveness of the proposed controller for the 3-DOF helicopter.