The invention discloses a phase loss protection device for a combined transformer. The phase loss protection device comprises a transformer, a left end connecting column, a phase loss protector, a connecting line and a phase line B, a phase line is mounted at the lower part of the transformer, a zero line is mounted on the right side of the phase line, a phase line C is mounted on the right side of the phase line B, the connecting line is mounted on the left side of the phase line C, emergency lamps are mounted on the surface of the connecting line, contactors are mounted above the connecting line, and a sensor is mounted at the upper part of the contactor. The emergency lamps are mounted on the surface of the connecting line, the contactors are mounted above the connecting line, the emergency lamp is connected between each phase of the phase loss protection device and the zero line, so that once the lamp is turned on to make an alarm, an electrician observes conveniently, the two contactors of 380V are connected to the phase lines AB and BC, one contactor is not actuated in case of phase loss, so that the sensor senses the working state of the contactor and transmits the condition to a signal receiver to implement the automatic power-off operation, then the degree of intelligence is high, the power can be cut off conveniently, and the requirement on electricity consumption of people is met.