A light modulation device and a single-channel spectrum detection system are provided. The light modulation device includes: a light guide plate; a dispersing component configured to disperse received light into light of different wavelengths and to diffract the light of different wavelengths into the light guide plate at different angles; and a dynamic filtering component configured to prevent light of a selected wavelength in the light guide plate from entering the dynamic filtering component such that the light of the selected wavelength emits out from the light guide plate, and to make light of non-selected wavelengths in the light guide plate enter the dynamic filtering component such that the light of the non-selected wavelengths is filtered out from the light guide plate.