Studying the sources of teachers' knowledge and the importance of different sources is of great significance to promote the development of teachers' knowledge. This paper systematically analyzes 27 empirical studies on the sources of teachers' knowledge in China and abroad in the past two decades or so in terms of methods and findings. The results show that the in-service experience of teachers contains more important sources than the preservice education and primary and secondary education. Teacher's experience and reflection, and exchanges with colleagues are the most important sources of teachers' knowledge development. Educational internships and practicums are the most important sources of teachers' knowledge during their preservice education, while other sources have no significant effect. The usefulness of teachers' knowledge sources is affected by variables such as knowledge category, subject, education stage and shows a certain degree of individual differences. The above results confirm the importance of teachers' practice, reflection, collaboration and exchange and indicate the necessity of improving preservice education. In terms of methods, it merits recommendation for future researchers in this area to use single-category-focused and topic-focused knowledge frameworks, more specific knowledge source frameworks, multiple ways of data collection, random selection of research subjects, and inferential statistical analysis. In addition, further studies should also look into the psychological and social-cultural mechanisms of teachers' knowledge development as well as the sources of teachers' knowledge.