The invention provides a PRONY analysis method and device for low-frequency oscillation of an electric system.The method includes the steps that a discrete linear prediction model is established based on discrete signals of the electric system; multiple discrete modes are calculated according to a characteristic polynomial of the discrete linear prediction model; energy values corresponding to the discrete modes are calculated; multiple modes are screened out from the discrete modes by comparing the energy values and serve as first dominant oscillation modes, and the low-frequency oscillation property of the electric system is analyzed according to the first dominant oscillation modes.The probability of erroneous judgment occurring when dominant modes are screened in a traditional PRONY analysis method can be reduced.