The invention discloses an electric leakage fault monitoring device for a power grid transformer, and the device comprises a main processor, a voltage transformer, a signal conditioning circuit, an alarm circuit, a bus self-taking power circuit, a wireless communication module, and a power module. The input end of the voltage transformer is connected with a load side of a transformer, and the output end of the voltage transformer is connected with the signal conditioning circuit. The signal conditioning circuit, the alarm circuit and the wireless communication module are respectively connected with the main processor. The bus self-taking power circuit is connected with the power module, and the power module supplies power to the device. The device timely reminds a maintainer of carrying out the processing, brings convenience to the maintainer for quickly searching a fault point, shortens the maintenance time, and reduces the economic loss. The power is obtained from a bus, so the power supply is convenient. Moreover, the device is provided with the voltage conditioning circuit, thereby enabling the output voltage to be stable.