Abstract: One method of conversion from whispered speech to formal speech based on the extended bilinear transformation is proposed.On account of the different deviation degrees of the whisper's formants in different frequency bands,the spectrum of the whispered speech will be processed in the separate partitions of this paper.On the basis of this spectrum,we will establish a conversion function able to usefully convert whispered speech to formal speech. Because of the whisper's non-linear offset in relation to normal speech,this paper introduces an expansion factor in the bilinear transform function making it correspond more closely to the actual conversion demands of whispered speech to formal speech.The introduction of this factor takes the non-linear move of the spectrum and the compression of the formant bandwidth into consideration,thus effectively reducing the spectrum distortion distance in the conversion.The experiment results show that the conversion presented in this paper effectively improves both the sound quality and the intelligibility of whispered speech.