Brain mechanism of metaphor processing has always been a focus in Neurolinguistics. This study approaches metaphor semantic representation mechanism of Chinese EFL learners of different proficiency levels by means of ERP technology. The results are the following: (1) Both of the two hemispheres are collaborated in metaphor processing with the left hemisphere serving a leading semantic recognition role. The left hemisphere is more sensitive to first language input, while the right hemisphere is more active to second language input. (2) Compared with Chinese learners with high proficiency in L2, learners with lower proficiency in L2 tend to adopt more Chinese neural mechanism in processing English metaphors. (3) When learners process metaphors, neural mechanism difference of learners with high proficiency in L2 is smaller than that of those with low proficiency in L2. The higher second language proficiency is, the higher degree of common representation of Chinese and English metaphor is.