Two kinds of new signal analyzing method that have appeared in recent years， ensemble empirical mode decomposition（EEMD） and Hilbert vibration decomposition（HVD）， are introduced into power system oscillation investigation. By referring to wavelet transform（WT） frequency spectrum， a review is made anew of the oscillation incidents in China Southern Grid（CSG） that occurred in recent years from the time-frequency point of view. The results show that the oscillation in question occurs in two forms， the non-stationary time-varying oscillation and stationary oscillation. It has been found that traditional analyses including the Prony method are incapable of handling non-stationary time-varying oscillation， whereas WT and HVD have broad prospects for application. It is proposed that HVD， WT and Prony should be complementary to each other in analyzing the oscillation incidents in CSG.