Aiming at the attitude stabilization control problem of hexacopters subject to unknown disturbance, a nonlinear feedforward compensation backstepping control method for attitude stabilization of hexacopter is proposed. The nonlinear unknown input observer is used to estimate the unknown external disturbance of the unmanned aerial vehicle. Then the Sigmoid tracking differentiator feedforward is introduced to compensate the estimated disturbance, which improves the attitude stabilization backstepping controller of the hexacopter. Furthermore, the stability results of the attitude tracking deviation closed-loop system are established. Some comparative simulation experiments verify the effectiveness and superiority of the proposed method.