Speech synthesis technologies have been widely applied in many applications. However, the flexibility to generate voices with different speaker's characteristics is limited, and only male and female voices can be usually chosen. When speech synthesis is applied on eBook, especially fairly tales and novels, it seems a little monotonous. Hence, this paper provides a brief review focusing on recent studies of the multi-voice speech synthesis technology. We expect that the multi-voice speech synthesis technology can be applied to develop audio-book applications with varied voices corresponding to different characteristics so as to improve the quality of listening in the future.