The disclosure provides a method and apparatus for adjusting wavelength for an Optical Line Terminal/Optical Network Unit (OLT/ONU). The method for adjusting wavelength for an OLT includes that: a source OLT sends an adjustment notification message to a target OLT, wherein the adjustment notification message is used for indicating that an ONU is to be adjusted into a Time-Wavelength Division Multiplexing Channel (TWDM CH) of the target OLT; and the source OLT receives an adjustment acknowledgement message provided by the target OLT, wherein the adjustment acknowledgement message is used for indicating that an adjustment process of the ONU has been completed. By means of the technical solution provided in the disclosure, an ONU of a source OLT can still work normally after being switched to a channel of a target OLT, thereby achieving the effect that the continuity of a service between the OLT and the ONU may be maintained.