Diplomatic discourse is an important medium for shaping national image. In light of critical discourse analysis, with the help of corpus methodology, this study analyzes the linguistic characteristics of China’s diplomatic discourse and the national image it constructs. Using the English translations of speeches delivered by the Chinese leaders at the General Debate of the UN General Assembly from 2012 to 2024 as the corpus, the analysis focuses on high-frequency words, keywords, and their collocations and concordances. The findings indicate that China’s diplomatic discourse has successfully constructed an image of China as a peace maintainer, development contributor, international cooperation promoter, and participant in global governance.