Flexible barriers, as one effective way to mitigate rock-fall hazards, have obvious advantages compared to the conventional concrete check-dams. It has been proved that a flexible barrier can perform well in trapping debris flow. In this study, an improved large-scale physical model for studying the impact of debris flow on a flexible barrier system is designed and constructed in Hong Kong. Some mechanical systems of the model are carefully designed to minimize the friction in door opening process. A comprehensive monitoring system has been specially designed and installed in this physical model. The system consists of conventional sensors (accelerometers, large tension-link force transducers, strain gauges on posts), special optical fibre sensors (small FBG tension-link force transducers, FBG basal friction transducers, FBG earth pressure cells), and high-speed cameras, high-frequency data-loggers, and computers. A single boulder impact test and a granular flow impact test were conducted using this large-scale physical model in order to evaluate the performance of the flexible barriers. In this paper, we will present the design and installation of this comprehensive monitoring system and selected test results.