A transformer anti-theft alarm device and an anti-theft alarm method thereof belong to the technical field of transformer substation anti-theft. According to the transformer anti-theft alarm device and the anti-theft alarm method thereof, a transformer which needs anti-theft is mounted and enclosed in an electronic detection anti-theft cage, and the electronic circuit signal in the anti-theft cageis monitored in real time through the microprocessor. When a theft operation occurs, the protected transformer assembly and circuit protection housing cannot be contacted if the anti-theft cage is not damaged, and the microprocessor will perform remote alarm through a network communication circuit and perform on-site alarm through a sound-light alarm circuit to play a warning role if the anti-theft cage is damaged. The transformer anti-theft alarm device and the anti-theft alarm method thereof solve the problems that an existing alarm device is poor in anti-interference performance, low in accuracy and not comprehensive in detection, and are suitable for anti-theft and use of a transformer.