We experimentally studied a passive optical network dynamic fault monitoring technology based on optical time domain reflectometry (OTDR), focused on various types of network structures with optical splitter (OS) devices, and analyzed the monitoring data with different lengths of fibers in front of the OS, such as 0, 14.5, and 50 km, respectively. Different from previous studies, we found that the new characteristics of echo curve can be used to realize the identification of different fault branches. We also make a detailed analysis on the feasibility of OTDR for multi-branch monitoring and the corresponding situation of instrument parameters. And the similar distance of the event situation is analyzed experimentally. We believe that these research data will provide effective technical reference for the intelligent management of optical networks in the current network.