WDM is one of the rapidly developed technologies in optical transmission．This paper analyses three protection mechanisms of WDM ring network，including the unidirectional wavelength channel protection， bidirectional wavelength channel protection，and the two-fiber optical multiplexing section bidirectional protection．This paper also presents a comprehensive comparison about the three protection mechanisms of WDM ring network．The conclusions may provides some theoretical guide on choosing the correct and effective protection mechanisms with different network environment．