Hydrate plugging and leakage are big issues in natural gas industry which can lead to huge economic costs, serious environmental destruction and life loss. In this paper, the acoustic reflection theories for leakage detection are studied and the chaotic characteristics of the detected signals are analyzed to distinguish hydrate plugging and leakage. A monitoring prototype system has been built for trials, in which incident acoustic waves are emitted into a pipeline by a transmitter and reflected waves caused by hydrate plugging or leakage are acquired by a receiver near the transmitter and amplified for further analysis. The experimental results demonstrate that the system can detect and locate both hydrate plugging and leakage at multiple positions online with good accuracy. Signal analysis results indicate that the difference in the chaotic characteristics of the detected signals for hydrate plugging and leakage could be used to distinguish the two types of abnormal events. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.