The present disclosure relates to the technical field of current sensors, and provides a fiber-optic current transformer based on nitrogen-vacancy (NV) centers in diamond, and a measurement method. The fiber-optic current transformer based on NV centers in diamond includes a device for laser light excitation and reflected light reception and analysis, a diamond NV center probe, a magnetic concentrator, and a microwave excitation device. The fiber-optic current transformer based on NV centers in diamond includes three measurement methods: an all-optical measurement method, a non-all-optical measurement method, and a measurement method combining the all-optical measurement method and the non-all-optical measurement method. A sensor in the present disclosure has advantages of a simple structure, strong practicability, resistance to external interference, and strong robustness.