It has been a long time since subsynchronous oscillation was first found in power system and has been threatening the power grid, being an important part of the stability problem of the power system. The oscillation detection method based on the measured data can let people know the original feature of a sub-synchronous oscillation accident, and can contribute to the oscillation source tracing and mitigating. The detection methods of sub-synchronous oscillation are various, and the effects of them are also different. In this paper, the signal preprocessing techniques for sub-synchronous oscillation are first summarized. Secondly, the signal identification techniques are summarized in 2 categories based on instantaneous value data and phasor data. Furthermore, a brief introduction to the newly emerging sub-synchronous oscillation weak segment positioning technology is made. Finally, some prospects are made to the field of the sub-synchronous oscillation signal detection.