This paper systematically reviews the studies of working memory in second language learning in China over the past 20 years. A total of 140 studies that were published in 13 major foreign language journals during the past 20 years (2000-2019) were categorized and analyzed according to research method, educational level, and research content. For research method, two phases could be identified: from 2000 to 2006, more attention focused on introducing theory and reviewing literature regarding the association between working memory and second language learning; and from 2007 to 2019, there is a growing body of quantitative and qualitative research. For educational level of the 75 empirical studies, the majority were targeted at adult learners, whose L2 proficiency was assumed to be at or beyond intermediate level. For the research content, they were classified into three dimensions: L2 understanding, L2 output, and the integration of L2 understanding and output. These three dimensions were sub-divided into a total of seven aspects: vocabulary, grammar, listening, reading, speaking, writing, and interpretation. Considerable advances have been made in the knowledge of working memory and second language learning. Nevertheless, more research is needed to develop a deeper understanding of the interrelationships between working memory and different domains of second language learning.