Learning idioms has always been difficult for L2 learners of English. Drawing on a cognitive linguistic perspective of idiom learning, this paper reports on an empirical study that investigated the effects of incorporating the knowledge of conceptual metaphor and metonymy in L2 classroom instruction of English idioms. The study confirmed the efficacy of applying the conceptual metaphor- and metonymy-based ways of teaching to Chinese college-level EFL learners. It further revealed the different degrees of teaching effect towards different types of metaphoric idioms. While no significant progress was made in learning orientationally and ontologically metaphoric idioms, students benefited more from the conceptual metaphor-based method in learning structurally metaphoric idioms. These findings serve to enrich L2 idiom pedagogy and provide EFL learners with strategies other than "rote memorization" in the process of idiom learning.