Embodiments of this application disclose a spectrum processing apparatus, which includes: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator (SLM), and a reflective element. Each port in the port assembly is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly is configured to adjust a width of the first light beam to obtain a second light beam. The reflective element is configured to reflect the second light beam to the dispersive assembly. The dispersive assembly is configured to decompose the second light beam into a plurality of sub-wavelength light beams. The reflective element is further configured to reflect the plurality of sub-wavelength light beams to the SLM. The SLM is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the reflective element.