The book takes conversational humor in situation comedies as the studying target and attempts to analyze humor from its pragmatic characteristics. It firstly gives an introduction to humor in four aspects: the definition of humor, the classification of humor, the functions of humor and the nature of humor. Thus, it's necessary and scientific to analyze humor language especially conversational humor from pragmatic aspect. Then it reviews the theoretical background concerning humor and mainly focuses on the Cooperative Principle. Since the whole research is based on the situation comedy Friends, the following chapter briefly discusses the relationship between situation comedy and humor, and then gives a brief introduction to the methodology and the chosen situation comedy-Friends. The main part of the thesis is the analysis of conversational humor in Friends. With plenty of examples selected from the 10 collections of Friends, a detailed analysis of conversational English humor and the pragmatic characteristics conveyed in it is given. The core of it is how the theory of conversational implicature is reflected in English humor in the form of conversations and how humor is produced.