Polysemy is a common existence in different languages. The meaning of vocabulary can generally be sorted into a "basic meaning" which is basic and frequently used and an "extended meaning" which derives from its basic meaning. In the semantic extension of vocabulary, the most basic and important cognitive modes are metonymy and metaphor. The thesis takes the Chinese word "頭" and the Korean word "머리" as objects on the basis of the definition in dictionaries, and it also analyses their characteristics of semantic extension with the theories of comparative linguistics and cognitive linguistics. According to what comes from the analysis, "頭" and "머리" share the same basic meaning and extended direction, that is, both can generally apply to people, items and abstract concepts. However, their extension methods and their concrete concepts in extension are not all the same. It is because that semantic extension is effected not only by internal factors of the language, but the external ones, for example, social circumstances, culture and technology development. The cognitive pattern of people in China varies from that of Korea due to cultural background of the two countries are not the same neither. Hence there are various differences in the semantic extension of "頭" and "머리".