Based on empirical research and qualitative analysis, this paper aims to explore the effects of L1 use on L2 vocabulary teaching. The results show that, during L2 vocabulary teaching process, the proper application of L1 can effectively facilitate the memorization of new words, and the bilingual method (both English explanation and Chinese translation) is welcomed by most subjects. Therefore, the use L1 as a means of semantization or as a tool for checking and validating L2 learners' understanding of word meaning should not be completely rejected, especially for adult Chinese EFL learners.