The invention discloses a flight control system of a small multi-rotor for power line patrol. The flight control system comprises an electronic compass, an angular rate gyro, a height sensor, an accelerometer, a GPS (Global Position System) receiver, a flight control computer and a ground control station. The electronic compass, the angular rate gyro, the height sensor, the accelerometer, the GPS receiver and the flight control computer are arranged on the multi-rotor. The electronic compass, the angular rate gyro, the height sensor, the accelerometer and the GPS receiver are connected with the flight control computer. The ground control station sends remote control commands to the flight control computer. The flight control computer comprises a data input module, an RS232 level switching module, an RS485 level switching module, a data storage SD card module, a smart fusion module, a power supply module, an automatic calling module, a recovery control module, a task device module and a steering engine module. The flight control system of the small multi-rotor for power line patrol has the advantages of improving the control sensitivity of the flying machines and facilitating system updating.