A frequency synthesis-based optical frequency domain reflectometry method to implement optical frequency domain reflectometry, comprising: performing an electro-optic modulation; on a local light, which is a non-swept optical signal with a constant frequency, by using a single frequency modulation signal, thereby obtaining multiple frequency components of an optical comb signal, and performing an acousto-optic modulation on the optical comb signal by using a pulse modulation signal, thereby simultaneously sweeping the multiple frequency components of the optical comb signal and thereby obtaining an optical pulse; inputting the optical pulse as a detection pulse optical signal to a test optical fiber; and detecting an obtained Rayleigh backscattered optical signal under coherent detection with the local light, and then performing a photoelectric conversion; using a photoelectric conversion module, collecting the detected signal by a data acquisition card as original data and performing a demodulation of the original data, wherein the demodulation comprises: generating a digital frequency-swept complex signal having segments as many as the frequency components thereof based on the original data, multiplying each of the generated multiple segments of the digital frequency-swept signal by a window function respectively and performing cross-correlation operations with the original data respectively to obtain multiple corresponding complex correlation functions, and obtaining a synthesis demodulation result of the multiple segments of the digital frequency-swept signal by adding the obtained multiple complex correlation functions directly. performing an electro-optic modulation; on a local light, which is a non-swept optical signal with a constant frequency, by using a single frequency modulation signal, thereby obtaining multiple frequency components of an optical comb signal, and performing an acousto-optic modulation on the optical comb signal by using a pulse modulation signal, thereby simultaneously sweeping the multiple frequency components of the optical comb signal and thereby obtaining an optical pulse; inputting the optical pulse as a detection pulse optical signal to a test optical fiber; and detecting an obtained Rayleigh backscattered optical signal under coherent detection with the local light, and then performing a photoelectric conversion; using a photoelectric conversion module, collecting the detected signal by a data acquisition card as original data and performing a demodulation of the original data, wherein the demodulation comprises: generating a digital frequency-swept complex signal having segments as many as the frequency components thereof based on the original data, multiplying each of the generated multiple segments of the digital frequency-swept signal by a window function respectively and performing cross-correlation operations with the original data respectively to obtain multiple corresponding complex correlation functions, and obtaining a synthesis demodulation result of the multiple segments of the digital frequency-swept signal by adding the obtained multiple complex correlation functions directly. generating a digital frequency-swept complex signal having segments as many as the frequency components thereof based on the original data, multiplying each of the generated multiple segments of the digital frequency-swept signal by a window function respectively and performing cross-correlation operations with the original data respectively to obtain multiple corresponding complex correlation functions, and obtaining a synthesis demodulation result of the multiple segments of the digital frequency-swept signal by adding the obtained multiple complex correlation functions directly.