Analysis methods for low-frequency oscillation are classified into two categories. One is the equilibrium-point eigenvalue method; the other is the mode extraction method along the disturbed trajectories. The former can be further sorted into deterministic linear models， deterministic non-linear models and probabilistic models. This category is independent of the disturbances. It can only show the dynamics near the equilibrium point， and is not suitable for systems with strong non-linearity， time variant， sequence fault or discrete actions. The latter extracts the oscillation information from the time response curves of the system. It can be further sorted into the signal processing method without knowledge on the system model， such as that for measured trajectories， and the piecewise autonomisation-linearization method， such as that for simulation results. Based on reviewing various methods， hopeful research areas are proposed.