An embodiment of the invention provides an online identification method of a low-frequency oscillation mode of an electric power system, an online identification device of the low-frequency oscillation mode of the electric power system and electronic equipment. The method comprises the following steps of based on operation measurement of the electric power system, sequentially using a stochastic subspace method and a clustering algorithm to obtain a first primary identification result; based on different combinations of operation measurement corresponding to the first primary identification result, obtaining a precise identification result of the low-frequency oscillation mode; based on each operation measurement of the electric power system, obtaining a second primary identification result; performing clustering analysis after the precise identification result is removed from the second primary identification result, and obtaining a missing mode; based on different combinations of theoperation measurement corresponding to the missing mode, obtaining a precise identification result of the missing mode; and using the whole of the two precise identification results as a final identification result of the low-frequency oscillation mode of the electric power system. The online identification method in the embodiment has the advantages that the low-frequency oscillation mode of theelectric power system can be more reliably, precisely and comprehensively identified, and the online monitoring of the low-frequency oscillation mode is realized.