Abstract: Duan Yucai and Wang Niansun are two distinguished persons in our linguistic history.As their represent works,ShuoWenJieZiZhu and GuangYaShuZheng have been widely accepted for their significant value in studying Chinese linguistic history.In this article,in view of the semantic extension of Chinese vocabulary,and started with these two persons' interpreting practice,we analyze their difference in the start point,the directing concept and the common terms,meanwhile,we summarize their similar cognition about the principles of semantic extension and the factors brought out the semantic variation.