The concept of bi xing (analogical and affective image) evolves with the dynamic relation between the original meaning and the derived meaning. Its development in the Tang dynasty could be examined better in Shige (Rules of Poetry), then prevailing poetic manual, than in the writings of Chen Zi'ang, Yin Fan, and others which have attracted most attention, as the former contains the discussions of different types of xing such as qi xing (image that raises the affect) and gan xing (image that stirs the affect). This article avoids explaining the early concept in terms of later usage and modern understanding. By situating the concept in its context in the Tang dynasty, the article analyzes how Tang poets viewed xing (affective image) as the beginning of poetry, more importantly, the original balladic qi xing and the relation between heart and thing, especially the type of gan xing where the thing stirs the heart, as considerably emphasized by modern scholars.