Once an actuator fault happens on a multi-rotor Unmanned Aerial Vehicle (UAV) the safety of the multi-rotor UAV the ground crew and the surroundings would be under threat.Fault reconstruction for actuator faults of multi-rotor UAV is beneficial to realize the fault-tolerant control and can improve the UAV safety and reliability.Firstly the actuator faults of the multi-rotor UAV is classified two kinds of faults such as actuator stuck and failing are analyzed and mathematical model of hexa-copter under actuator faults is built up.Secondly fault reconstruction based on adaptive observer is designed.By selecting suitable adaptive law the nonlinear observation parameters can be regulated automatically and the reconstruction to the fault information can be achieved accurately.The simulation validates the accuracy of the fault reconstruction methods.