In order to improve the control accuracy of attitude angles and enhance the anti-interference ability of unmanned helicopter, a novel ESO-LQG-PI control method for TREX 700L helicopter is proposed in this paper. By considering the high non-linearity of the helicopter system, a class of small disturbance incremental linearization processing approach is adopted. Meanwhile, an extended state observer (ESO) is used to estimate and compensate the system disturbance in real time. The proportional integral (PI) controller is added to reduce the steady-state error caused by input signals, then linear quadratic Gaussian (LQG) controller is presented to obtain the optimal control gain. Summing up the advantages of PI and LQG, this paper proposes an ESO-LQG-PI control method. The experimental results show that the hovering attitude controller of unmanned helicopter improves the control precision of the control system, the error range of attitude angle is ±0.5°. It can realize the hovering control of the helicopter well, and has anti-interference ability.