Abstract: Based on image schema theory and conceptual metaphor theory，this paper analyzes the cognitive semantics of phrasal verbs.It claims that the particle up has both spatial and metaphorical meanings，and that the meanings of the verb and of the particle are essential to phrasal verbs.It is shown that“V＋up”generally means that a force acts upon an entity and forces the latter to change in terms of location，quantity，shape and state.Semantically，this structure expresses causative meaning，which is realized by mapping the spatial domain onto mental and social domains.This paper provides a new explanation of transitive phrasal verbs from the cognitive perspective.