Abstract: The bringing changes of pitch and syllable duration marking stresses in clauses that are put in discourses were observed in the recitation of Chinese News broadcasting text.As compared isolated clauses with them in a discourse, the results show that the pitch changes of intonational nucleus in clauses are most prominent,i.e.top lines of pitch move downwards as a whole.The weakened degree is different to different kind of stress.The stress of clause in a discourse will be obviously weakened,if it wasn't assigned discourse stress;The weakness is presented by to reduce the pitch and syllable duration in same time.The speakers could to use the modification of the clause stress in a discourse which consists of some clauses,in order to control the discourse prosody,and then to glibly express the meaning of text.It introduced the experimental phonetics to broadcasting speech education;and provided a prosodic control for the new Chinese TTS system.