Abstract: The analysis of exponentially forgetting transform (EFT) is made in this paper. The application of a sliding single-sided exponential window, make it possible the iterative operation in EFT which greatly raises computation efficiency. Compared with other time-frequency distributions, EFT is especially useful in case of large data length and more suitable for hardware implementation. The relationships of bias and mean square error of EFT with SNR and forgetting coefficient are studied. And in order to overcome the drawbacks of single-sided window, a new time-frequency distribution using double-sided exponential window which is computation efficient with much bias reduction is introduced.