West monks (番僧) and foreign monks (蕃僧) are two keywords with deep implicitness in the history of Chinese Buddhism. Many of the west monks and foreign monks have taken the messengers’ role in Dharma transmission that has been verified by a variety of historical records. Nonetheless some scholars regard west monks and foreign monks as synonyms so that it is impossible for others to understand exactly the relevant meanings in the materials. This thesis aims at an analysis of the lexicon based on west (番) and foreign (蕃) in order to clear the implications and even the truth of the two words in historical context. The arguments also refer to other keywords such as western Tibeto-Burman peoples (西番), tribal generals (蕃將), exotic monks (胡僧), pure monks (梵僧) and western monks (西僧) before interpreting the significance which alien culture contributed to the linguistic construction.