Prosodic prediction, which is a process of prosodic chunking, is one of the major factors for the naturalness of speech synthesis. In this study, prosodic segmentation of spontaneous speech material is done through perception at first, and investigation of the prosodic structure shows that prosodic chunking is constrained by rhythm and parts of speech. Some constraints for prosodic chunking are discussed in this paper, and an OT analysis is done on the chunking process.