The invention discloses a battery automatic replacement system of a small-sized multi-rotor-wing unmanned aerial vehicle. The battery automatic replacement system comprises a multi-track trolley, a battery storage disk, an unmanned aerial vehicle landing gear, a landing gear fixing plate, a landing gear fixing plate support, a battery storage disk support and a mechanical arm, wherein the landing gear fixing plate is arranged above the multi-track trolley, and is fixedly connected with the multi-track trolley through the landing gear fixing plate support; the unmanned aerial vehicle landing gear is arranged above the landing gear fixing plate; a battery inlet matched with the size of a battery is formed in the center of the fixing plate; the battery storage disk is arranged below the landing gear fixing plate, and is fixedly connected with the multi-track trolley through the battery storage disk support; and the mechanical arm is arranged below the battery storage disk. The battery automatic replacement system adopts a turntable type battery storage bin, so that five times of battery replacement can be performed at most through one step; and the battery automatic replacement system adopts a blind plugging type battery installation mode to achieve effects of convenience, fastness and high efficiency.