”Grammaticalization” is an important topic in historical linguistics. It reflects the process of words or structures changing to be functional components. This paper focuses on the Chinese suffix tou. It observes derivations with tou and tou's gramaticalization from syntax, semantics and pragmatics. We chose Chinese Buddhistic Scriptures from the former Han Dynasty to the Ming Dynasty, i.e. Middle and Modern Chinese, as materials. In addition, we also included the data in the middle area to make comparison with Buddhistic Scriptures. According to the study of this paper, the grammaticalization of tou is a metaphor: from shift in space to shift in time. The Gramaticalization of tou, which changes from a lexical word to a suffix, is the result of metaphor, metonymy, analogy and generalization.