Signal sending method and apparatus. The signal sending method includes: sending, by a first apparatus, an optical signal to a second apparatus in a slot before a first wavelength slot; sending, by the first apparatus, a first optical signal to the second apparatus in the first wavelength slot; and sending, by the first apparatus, an optical signal to a second apparatus in the slot after the first wavelength slot. A wavelength of the first optical signal is a first wavelength. The first optical signal sent by the first apparatus in one first wavelength slot is used to carry first wavelength data on one symbol. Wavelengths of the optical signals sent by the first apparatus in the slots before and after the first wavelength slot are wavelengths other than the first wavelength.