In order to control multi-rotor aircraft to hover stably and precisely over a fixed point,position and attitude controllers are designed by using cascade PID to control the position and attitude of the multi-rotor aircraft.A mathematical model is established after kinematics and dynamics analysis of the multi-rotor.Based on the analysis of the modela control allocation model is established.In order to simplify the design of controllersthe controllers are divided into two partsnamelyposition and attitude controller and control allocator.Changing the control allocator can realize the flight control of different rotorswhich has wider applicability.Simulation results show that the multi-rotor UAV has fast response speed with the stages of vertical take-off and level flight connected closelyand can accurately reach the given target point and hover stably over it.