The invention relates to a photon differential protection device. The photon differential protection device is characterized by comprising a light source, an optical fiber coupler, a multimode fiber, a first optical current sensor, a second optical current sensor, a polarization-maintaining optical fiber and an electronic processing unit; the first optical current sensor and the second optical current sensor are arranged at two ends of a protection interval respectively; a light signal P0 which is emitted from the light source is transmitted to the optical fiber coupler through the multimode fiber to be divided into two beams of light P0a and P0b with the same power; the P0a and the P0b are transmitted to the first optical current sensor through the multimode fiber; the current in the protection interval is detected through the first optical current sensor and the second optical current sensor; the first time of polarization and rotation is performed on the P0a and the P0b through the first optical current sensor according to the detected current; the first polarized light and the second polarized light after the rotation are transmitted to the second optical current sensor and the second time of rotation and light detection are performed; a first light signal Pax and a second light signal Pbx which are obtained are transmitted to the electronic processing unit to be processed; the processed result is in comparison with a preset value through the electronic processing unit to achieve the judgment of the fault of the protection interval. The photon differential protection device can be widely applied to smart power grids.