The invention relates to the technical field of optical fiber sensing, in particular to a current transformer with a measuring light path. The current transformer comprises a light source, a first coupler, a second coupler and a photodetector; the first coupler is provided with a first output end, a light signal input end and an input and output end; the second coupler is provided with a first input end, a reflected light output end and a reflected light testing end; the first output end is in optical fiber connection with the first input end; the reflected light testing end is used for beingconnected with a reflected light testing device to test a reflected light signal; and the reflected light signal is divided into a testing part and a measuring part by the second coupler. When the photodetector generates the phenomenon of no output, the reflected light testing device can directly test, thus whether the photoelectric detector breaks down or not is judged, and the problems that in the fault detection process of active devices in the full-optical-fiber electronic current transformer, due to disassembling and fiber breaking, detection is inconvenient, and a light path structure ofthe transformer is seriously affected are solved.