Discourse during the routine press conference held by the diplomatic service of each country is typical diplomatic discourse,bearing unique characteristics. Interpersonal negotiation between the speaker and reporters plays an important part. Based on the theories of the systemic functional linguistics,this paper analyzes the interpersonal metaphor( including metaphor of mood and metaphor of modality) in the Sino- US diplomatic discourse and explores different functions of interpersonal metaphor against different cultural backgrounds. Discourse during the routine press conference held by the diplomatic service of each country is typically diplomatic discourse, bearing unique characteristics. Interpersonal negotiation between the speaker and reporters plays an important part. Based on the theories of the systemic functional linguistics, this paper analyzes the interpersonal metaphor (including metaphor of mood and metaphor of modality) in the Sino-US diplomatic discourse and explores different functions of interpersonal metaphor against different cultural backgrounds.