The invention discloses an electric system low-frequency oscillation mode parameter identification method. The method includes the steps that firstly, interconnecting tie power signals recorded by a wide-area measuring system in an electric system are read; the read power signals are processed, and then corresponding power fluctuation signals are acquired; then the fluctuation signals serve as input signals based on the random decrement technology, and free attenuation response signals of the system are acquired; finally, based on a total least square rotation invariant sub-space parameter estimation method, mode identification is conducted on the free attenuation response signals, low-frequency oscillation mode frequency and the damping ratio are identified, and the electric system low-frequency oscillation mode parameter identification method based on the random response signals has the technical advantages of being high in noise immunity and identification accuracy.