Embodiments of this application disclose an optical amplification apparatus and a multi-port wavelength division multiplexing coupler, configured to amplify an optical signal. The optical amplification apparatus in embodiments of this application includes: a first pump source, where the first pump source is configured to provide first pump light, the first pump light is configured to amplify a plurality of first optical signals; a first multi-port wavelength division multiplexing coupler, where the first multi-port wavelength division multiplexing coupler is configured to couple the plurality of first optical signals and the first pump light; and an active optical fiber connection cable, where the active optical fiber connection cable includes an active doped fiber for transmitting and amplifying a plurality of third optical signals, and the plurality of third optical signals are optical signals obtained by coupling the plurality of first optical signals to the first pump light. In embodiments of this application, the optical amplification apparatus couples first optical signals with different wavelengths through a multi-port wavelength division multiplexing coupler, to amplify the first optical signals with different wavelengths, thereby reducing a size of an optical amplifier.