The invention provides a spectrometer based on a fiber grating time domain reflection technology, and belongs to the technical field of a fiber grating spectrometer. The spectrometer comprises a light source to be detected, an optical modulator, a data collecting and processing unit and the like; the spectrometer is characterized in that: the optical modulator is located behind the light source to be detected and the back side of the optical modulator is connected with one input end of a 2*2 optical fiber coupler through optical fibers; one output end of the 2*2 optical fiber coupler is connected with a fiber grating group through optical fibers and the other output end of the 2*2 optical fiber coupler is connected with a photoelectric detector through optical fibers; the other input end of the 2*2 optical fiber coupler is connected with the photoelectric detector through optical fibers; the output end of the photoelectric detector is connected with a signal reforming and amplifying circuit and the output end of the signal reforming and amplifying circuit is connected with an interface of the data collecting and processing unit; and electric signals which are sent out by the photoelectric detector are reformed and amplified and then are transmitted to the data collecting and processing unit to carry out signal processing. The spectrometer provided by the invention has the characteristics of simple and rational structure, small volume and low cost.