There are a lot of metaphors in Korean and Chinese idioms, which come from both nations’ cognition and reflection of realistic world and possess evident national color. According to views of cognitive linguistics, some metaphorical reflection has universality and some have specialty and only exist in specified culture. Korea and China have different national cultures and language view, so metaphors in the two countries’ idioms have different features. we think that idiom is the product of all human beings’ cognitive activities and most Korean and Chinese idioms are metaphorical. This study makes trial exploration of understanding and emergence mechanism of Korean and Chinese idioms with research achievements of modern metaphor theory from the perspective of cognitive linguistics, thinking that idiom is the result of applying metaphorical thoughts in the process of cognition. Metaphor is not only a kind of rhetorical device in language but also an important thinking way through which human learn about the world. Metaphorical thought can improve with the improvement of human being’s cognitive capacity and it is advanced stage of human’s cognition. It is proper to say that the essence of metaphor is illustrating things in one field with experience of another field. People’s concept is based on this. Metaphor phenomena can be seen everywhere, because human’s language include a large number of metaphors, which are very universal. Metaphors behind Korean and Chinese idioms not only are rhetorical devices by means of form vivid expression of language but also, more importantly, are based on experiences. Experience of daily life is the gap that connects object things in different domains.