Abstract: Embodiments provide a fault locating method for an optical network and a related device to reduce network complexity of fault locating and improve accuracy and efficiency of fault locating in an optical network. The method provides a network management device obtains a first sample set from a first optical network device, where the first sample set includes a plurality of optical powers obtained from the first optical network device sequentially sampling a first optical signal for a plurality of times by the first optical network device in a first fault locating time period, and at least one optical power included in the first sample set is less than or equal to an optical power threshold. The network management device determines a fault type in an optical network based on a change trend of the plurality of optical powers.