The present invention discloses an outdoor power transformer monitoring alarm device. The outdoor power transformer monitoring alarm device includes a power transformer installed outdoor, an electromagnetic switch, mutual inductors, a driving circuit, current detection circuits, a voltage detection circuit, a microprocessor, an alarm horn, an indicating lamp and a mobile phone module; the high voltage side of the power transformer is connected in series with the electromagnetic switch; a high-voltage line is provided with the mutual inductors; a power transformer grounding line is provided with the mutual inductor; a temperature switch and an oil level sensor are arranged in the power transformer; the mutual inductors are connected with the microprocessor through the current detection circuits; the temperature switch and the oil level sensor are connected with the microprocessor; the output end of the voltage detection circuit is connected with the microprocessor; and the microprocessor is connected with the electromagnetic switch, the alarm horn, the indicating lamp and the mobile phone module. The outdoor power transformer monitoring alarm device of the invention has the advantages of reasonable design, simple structure and easiness in manufacture. With the outdoor power transformer monitoring alarm device adopted, information of the power transformer, such as over voltage, overload, electric leakage, excessively high working temperature and oil shortage, can be detected automatically; and if abnormal situations appear, on-site alarm signals and remote alarm signals can be emitted.