The modal adverb “ke”（可）in Modern Chinese originated from the auxiliary verb “ke” （可）.In Han Dynasty modal adverb “ke”（可）was in the embryonic stage and it matured in the middle ancient times. Firstly it expressed the imperative mood, and gradually it stressed the talker’s subjectivity. In Qing Dynasty the modal adverb “ke”（可）had a new usage. It could modify adjective and in the type of sentences “ke”（可）was phonetically stressed. It was the grammaticalization process of “ke”（可）.