According to Lakoff et al, metaphor is the main mechanism through which we comprehend abstract concepts and per?form abstract reasoning. As a great poet, Robert Frost realized the cognitive functions of metaphors and used them frequently and skillfully in his poetry. By doing so, he was able to convey abstract and philosophical reflections through simple language and en?rich the theme of his poetry. This thesis conducts a survey of the definitions of metaphors and makes an analysis of the metaphors employed by Frost in his poetry, trying to answer two questions:1) How does the use of metaphor help to convey the poet’s ab?stract and profound philosophical reflections? 2) How does the use of metaphor help to enrich the themes of Frost’s poetry?