Optical fiber acoustic sensor has attracted a significant amount of research attentions in recent years. A key issue for all optical fiber acoustic sensors is to improve the quality of detected signal. In this work, a novel wavelet packet speech signal retrieving method is proposed for improving detection performance of optical fiber acoustic sensors. The experiment system of optical fiber acoustic sensing is set up based on the principle of optical fiber interferometer. The experimental results show that the new threshold processing method improves the signaltonoise ratio compared with hard threshold and soft threshold processing method. Furthermore, the continuity of speech signal is guaranteed and the speech quality is improved. The proposed method can be widely used for a variety of speech detecting applications, especially for realtime speech detecting.