The invention discloses an automatic control system of an unmanned aerial vehicle (UAV). The automatic control system comprises a processor unit, a controller, a first motor, a second motor, a third motor, a fourth motor, a signal processor and an unmanned aerial vehicle, wherein the processor unit transmits control signals to the controller; the controller divides the control signals into a first driving signal, a second driving signal, a third driving signal and a fourth driving signal; and the first driving signal, the second driving signal, the third driving signal and the fourth driving signal are used for controlling the first motor, the second motor, the third motor and the fourth motor respectively, and the first driving signal, the second driving signal, the third driving signal and the fourth driving signal which pass through the first motor, the second motor, the third motor and the fourth motor are compounded by the signal processor to control the movement of the unmanned aerial vehicle. The automatic control system of the UAV breaks through the limitation of high-voltage line patrol of 'giving priority to helicopter patrol and giving supplement to manual patrol' in the prior art.