A wavelength division multiplexing passive optical network, comprising an optical line terminal and at least one optical network unit, wherein: the optical line terminal comprises at least one optical transmitting module, the optical network unit comprises an optical receiving module, a one-to-one mapping is established between the optical transmitting module and the optical receiving module; the optical transmitting module is adapted to split a light with a wavelength of λ from the same optical source into two optical signals, a first optical signal is modulated and used as a downlink carrier signal, and a second optical signal unchanged loops back from the optical network unit, and is used as an uplink carrier signal, wherein the optical transmitting module of the optical line terminal comprises: a shared optical source, an optical splitter, an optical multiplexer, a modulator, a division selector and an optical receiver; wherein, the optical splitter is adapted to split a continuous light with a wavelength of λ from the optical source into the two optical signals, the first optical signal enters the modulator as the downlink carrier signal, and the second optical signal enters the optical multiplexer directly; the modulator is adapted to modulate a downlink signal to the first optical signal and then input a modulated downlink signal to the optical multiplexer, where a central wavelength of the modulated downlink signal has an offset of a preset value Δλ compared with a central wavelength of the second optical signal; the optical multiplexer is adapted to multiplex the modulated downlink signal with the second optical signal, and send a multiplexed signal to the optical network unit via the division selector; and the optical receiver is adapted to receive an uplink signal sent by the optical network unit via the division selector; the optical receiving module is adapted to receive the multiplexed signal comprising the modulated downlink signal and the second optical signal from the optical transmitting module, separate the multiplexed signal and use the second optical signal received as the uplink carrier signal to transmit the uplink signal. the optical line terminal comprises at least one optical transmitting module, the optical network unit comprises an optical receiving module, a one-to-one mapping is established between the optical transmitting module and the optical receiving module; the optical transmitting module is adapted to split a light with a wavelength of λ from the same optical source into two optical signals, a first optical signal is modulated and used as a downlink carrier signal, and a second optical signal unchanged loops back from the optical network unit, and is used as an uplink carrier signal, wherein the optical transmitting module of the optical line terminal comprises: a shared optical source, an optical splitter, an optical multiplexer, a modulator, a division selector and an optical receiver; wherein, the optical splitter is adapted to split a continuous light with a wavelength of λ from the optical source into the two optical signals, the first optical signal enters the modulator as the downlink carrier signal, and the second optical signal enters the optical multiplexer directly; the modulator is adapted to modulate a downlink signal to the first optical signal and then input a modulated downlink signal to the optical multiplexer, where a central wavelength of the modulated downlink signal has an offset of a preset value Δλ compared with a central wavelength of the second optical signal; the optical multiplexer is adapted to multiplex the modulated downlink signal with the second optical signal, and send a multiplexed signal to the optical network unit via the division selector; and the optical receiver is adapted to receive an uplink signal sent by the optical network unit via the division selector; wherein the optical transmitting module of the optical line terminal comprises: a shared optical source, an optical splitter, an optical multiplexer, a modulator, a division selector and an optical receiver; wherein, the optical splitter is adapted to split a continuous light with a wavelength of λ from the optical source into the two optical signals, the first optical signal enters the modulator as the downlink carrier signal, and the second optical signal enters the optical multiplexer directly; the modulator is adapted to modulate a downlink signal to the first optical signal and then input a modulated downlink signal to the optical multiplexer, where a central wavelength of the modulated downlink signal has an offset of a preset value Δλ compared with a central wavelength of the second optical signal; the optical multiplexer is adapted to multiplex the modulated downlink signal with the second optical signal, and send a multiplexed signal to the optical network unit via the division selector; and the optical receiver is adapted to receive an uplink signal sent by the optical network unit via the division selector;