波分复用无源光网络(WDM-PON)被认为是有前途的宽带接入网技术。随着网络架构复杂度的不断增加和规模的不断扩大，为了保证网络接入的可靠性和可维护性，对于高质量可靠的系统，WDM-PON 物理层的监测问题至关重要。波长可调谐光时域反射计(OTDR)是WDM-PON 光纤链路监测中最为有效的方式，但是由于WDMPON光纤链路结构复杂度的提升，它也面临许多挑战。通过分析WDM-PON 的结构特点和监测需求，介绍了目前主要的基于波长可调谐OTDR 的研究进展以及其他技术在波长可调谐OTDR 中的应用。

The wavelength-division-multiplexing passive optical network (WDM-PON) is considered as a promising technology for passive optical network (PON). With the increase of complexity and the expansion of scale, to ensure access network with the reliability and maintaining, the search for the physical-layer WDM-PON monitoring is therefore becoming crucial to the high quality and reliable system. The tunable optical time-domain reflectometry (OTDR) is an effective way, however, due to the complexity of WDM-PON fiber link, tunable OTDR also faces many challenges. By addressing the features of WDM-PON structure and major requirements of WDM-PON monitoring techniques, the research advances of tunable OTDR and the application of other technologies which are used for tunable OTDR are reviewed.