The invention relates to a low-frequency oscillation monitoring technology of a large-scale electrical network on the basis of a wide area measurement system (WAMS). The invention combines the advantages of various real-time analysis algorithms in allusion to the limitation that the low-frequency oscillation monitoring system in prior art only can perform offline analysis, so as to disclose an online low-frequency oscillation monitoring system of an electrical network to realize the online monitoring and analysis of the low-frequency oscillation of the electrical network. The low-frequency oscillation monitoring system of the electrical network of the invention is a software function module based on a traditional WAMS system, and comprises a system management module, a data communication module, a real-time monitoring module, a data analysis module and a database module. The invention realizes the real-time recording, real-time displaying and stable analysis functions of the low-frequency oscillation data in the electrical network, and is mainly used for the monitoring and analysis of the large-scale electrical network.