Abstract: In modern Chinese language, ‘yexuba’ is often used independently and its discourse distribution is flexible. Research has found that the discourse function of ‘yexuba’ is closely related to its distribution. Different sequence positions reveal different discourse functions. ‘Yexu’ becomes an evaluation marker through subjectivization and inter-subjectivization. It has been reanalyzed with the synonym of ‘ba’ to form ‘yexuba’. ‘Yexuba’ is often seen in dialogues, and the interactive reorganization of linguistic resources is a significant driving force for its emergence. Through processes of integration and standardization, the functional fusion is completed. Besides, through typological investigation, this article finds that the combination of modal adverbs and modal particles exist not only in Chinese, but also in other ethnic languages of the Sino-Tibetan family.The commonality of modal function serves as the foundation for their fusion, and iconicity is the fundamental driving force for their fusion.