Abstract: This paper concerns the principle of speech output interface of a robot.Somemain issues,as follows,are detailed in the article,(1)selection of basic acousticunits which can be concatenated to generate utterances,(2)the rule of tonal modification,(3)consonant-vowel transition,and (4)hybrid formant synthesizer.Thetest written in Chinese phonetic symbols is conveyed into the system and the speech onunlimited vocabulary will be delivered by rule.