An embodiment of the invention relates to the field of quantum communications, and more particularly, to a quantum key distribution method, a transmission device, and a reception device used to more accurately recover an original key in a quantum key distribution process. In the embodiment, a frequency of a pulse contained in a first optical pulse signal is greater than a frequency of a pulse contained in a second optical pulse signal, and thus a time interval between a pulse of a quantum optical signal and a pulse of an adjacent reference optical signal is short. Accordingly, when a reception device measures the pulse of the reference optical signal and a local oscillator optical signal to obtain phase/frequency information therebetween and to estimate phase/frequency information between the pulse of the quantum optical signal and the local oscillator optical signal, the information is more reliable. The more reliable phase/frequency information between the pulse of the quantum optical signal and the local oscillator optical signal enables more accurate modulation of the local oscillator optical signal used to perform coherent coupling on the quantum optical signal, such that an original key recovered from the quantum optical signal is more accurate.