This paper proposes a design method of robust fault reconstruction for a 3‐DOF helicopter with actuator faults and disturbance. The model of the 3‐DOF helicopter considered in this paper is an affine nonlinear system. An adaptive sliding mode observer is firstly proposed such that the actuator fault can be reconstructed through the adaptive law online. Then, based on linear matrix inequalities (LMI), a feasible algorithm is explored to solve the designed parameters. Finally, a simulation study of the 3‐DOF helicopter is presented to show the effectiveness of the scheme.