Abstract: Owing to the lack of telephone speech data, this paper proposes a software simulation implementation of converting clean speech sounds into telephone-quality ones. Filter design technology is adopted to simulate the frequency response characteristics of various analogue transmission equipments in telephone circuit connection and to make simulation study on such telephone speech phenomena as different noise behaviours in telephone channels. The spectral distortion analysis and recognition experiment results show that through the reasonable setting and regulating, the algorithm can effectively realize the approximate simulation from clean speech to telephone-quality ones so that the simulated speech sounds generated from clean data can achieve as good recognition performance as real speech.