Abstract
Humor, as an essential merit of human communication,makes our life more interesting. Based on Incongruity Theory in psychology,humor is generated by incongruity between what we expect to happen and what actually happened. Accordingly, this thesis focuses on the interpersonal function in systemic functional grammar and explores the humorous dialogues in a famous American sitcom the Big Bang Theory in terms of the functional structure and components. This thesis makes an attempt to demonstrate the applicability of taking interpersonal function theories into humor analysis.