Abstract: Using online grammaticality judgment tasks and choosing Chinese English learners of different English proficiency as subjects, this paper explores the processing mechanism of English binomials with different frequency and lexical semantic relations of component words. The results show that 1) there is a frequency effect on the processing of binomials of English learners; 2) the lexical semantic relations of component words have a moderating effect on the frequency effect. In binomials of antonym relations, the subjects’ reactions to high-frequency ones are faster and the error rate is lower than low-frequency ones; 3) the moderating effect of the lexical semantic relations of component words is influenced by the learners’ English proficiency level. The study shows that binomials are psychologically realistic to some extent, which supports the hypothesis of the usage-based view on L2 acquisition. However, the lexical semantic relations of component words and the learner’s English proficiency level affect the storage of the chunks in the mental lexicon.