In order to better reflect and meet the actual operation and flight demand of multi motor unmanned helicopter, the problem of attitude control for the helicopter with flight state constraints is discussed, taking into consideration of uncertain and external disturbance factors. Firstly, the mathematical model of the unmanned helicopter is given by Newton Euler formulas. Secondly, a SMDO disturbance reconstruction algorithm is designed to reconstruct the unknown compound interference in the attitude system and to design the compensation control law. Thirdly, in order to address the state constraints and avoid the differential expansion in design of back stepping controller, an attitude controller based on the SMDO disturbance compensation and constrained command filter is designed. Finally, the correctness of the designed algorithm is verified through simulation experiment.