This study takes 改革 gaige and reform as two significant sociocultural keywords and adopts a historical semantics approach in examining the two words. The two words’ diachronic changes and their current lexical behaviors are described from a comparative perspective. Rich historical and cultural information of two societies has been uncovered through studying the two keywords. The first section of the paper is devoted to an introduction to keywords study and a review of studies on reform and gaige. The second part proposes two research questions about the diachronic changes and contemporary use of gaige and reform, and demonstrates our research methods. The third section presents major research findings from the aspects of etymology and lexical properties. Section four discusses the results relating to broader social cultural contexts in China and the English-speaking communities. The conclusion section summarizes our main findings and proposes a new approach for keywords study named “corpus-assisted critical keywords study”.