Abstract: A relic of ancient Chinese, De Xing has lexicalized and is wide used in Southwest Mandarin. The lexicalization of De Xing is the fruit of grammaticalization of De and Xing:De bore the meaning of "able" in the pre-Qin era; Xing lost its lexical meaning in the Qing dynasty and began to have the modality meaning of "permission".De Xing gradually ceased to exist after its lexicalization but was reserved in Southwest Mandarin. The lexicalization of De Xing was the result of changes in the lexical meaning and syntactic environment, and the rise of frequency of use, which in fact is a transition of meaning from the objective domain to the subjective domain. Currently,the grammatical function of De Xing is still evolving,with De losing its lexical meaning and converting from a transitive word to an intransitive word and transiting from the objective domain to the subjective domain. And with the increase in the frequency of use of De Xing, its negative form Bu De Xing is likely to be lexicalized.

Key words: Southwest Mandarin, De Xing, lexicalization, subjective domain, ancient Chinese