English phrasal verbs are widely believed to be particularly difficult to master because the choice of verb-particle combinations seems so unsystematic.The tendency in the past has been to regard them as arbitrary items of language that must simply be learned by heart,i.e.rote memorization.According to cognitive linguistics,however,those combinations are in fact motivated and can be analyzed and systematized.This paper aims to explore the cognitive motivation of the sense formation and expansion in the verbal phrases,with the principles of prototype,ideal cognitive model and cognitive domain,image schema,metaphor,and give an interpretation about the principles of motivation in the formation of verbal phrases in order to provide a cognitive approach to the understanding of English verbal phrases.