Abstract: In WDM optical network,wavelength is the unit of transmission and switching.which is the limited network sources,so the research of wavelength assignment algorithm becomes a focal topic,With efficient algorithm,the utilization factor for wavelengths can be improved greatly and the bandwidth resources in WDM can be made full use of.Several static and dynamic wavelength assignment algorithms are presented in detail.Especially to larger mesh networks,several kinds of dynamic wavelength assignment algorithms are introduced.For the usage of wavelength converter,a layered-graph approach,is put forward,which can soluve routing and wavelength assignment simultaneously,is put forward and is fit for random wavelength converters and WDM optical network.