As bilinguals have increased in number these years, bilingual speech production (BSP) has become a hot topic in psycholinguistic research. The exploration of BSP can not only reveal the psychological mechanism of language processing but also help to understand the general mechanism of information selection in the human cognitive process. Language-switching has currently emerged as one of the primary research paradigms for studying multilingual speech production. Therefore, this paper summarizes several experimental designs of the language-switching paradigm, analyzes observations found in the experiments, summarizes the four theoretical models proposed in the previous literature, and finally puts forward possible future orientations on the basis of current research.