This paper carries on a tentative interpersonal metafunction analysis of Barack Obama's victory speech from the interpersonal metafunction, which aims to help readers understand and evaluate the speech regarding its suitability, thus to provide some guidance for readers to make better speeches. This study has promising implications for speeches as follows: (1) Positive declarative clauses are recommended to convey information and convince the audiences with positive facts. (2) Modal verbal operators with high modal commitment can show the addresser's firm determination to finish tasks and build up the addresser's authority. (3) The frequent applications of "we" and "we"-"you"-"we" pattern help to create an intimate dialogic style, which can shorten the distance between the addresser and the audience and further persuade the audience to share the same proposal of the addresser.