Flexible thin-wall bearing (FTB) is forced to deform with the elastic deformation of the flexspline in motion, resulting in a completely different fault characteristic frequency (FCF) from ordinary rolling bearings. However, current extraction methods treat FTB as an ordinary one and are analyzed based on spectrum, without considering the time-varying nature of FCF in FTB. In an effort to address this concern, this paper proposes a Gini index-based time-reassigned multisynchrosqueezing transform, where the window size is determined by the period impulses feature in the noise-removed signal. In addition, a frequency point selection method that contains fault characteristics of FTB is proposed by calculating the maximum correlated kurtosis in time-frequency plane. Furthermore, the instantaneous frequency is extracted by calculating the time interval between two consecutive impulses. The extracted fault frequency well agrees with the experimental result and outperforms the frequency obtained by other time-frequency analysis techniques.