Researchers realize that teachers need to possess knowledge from various scopes including pedagogical content knowledge (PCK). The components of PCK include subject knowledge and general pedagogical knowledge. PCK does not only comprise the knowledge of teaching materials, but also the expression of subject knowledge in the most representative mode in regard to teachability. PCK as unique knowledge of teachers. Its features include that teachers need to fully grasp the subject content knowledge and understand students’ learning characteristics. Then teachers express the subject content knowledge through effective strategies in order to ensure students’ understanding, inquiry and construction of knowledge. This paper, reviewing relevant literatures since 2000, tries to synthesize empirical... research on PCK and briefly illustrates the research finding. From the literature review, the authors note that there are three main ideas about PCK: teachers understand the specific subject content; teachers manage and utilize specific representation of subject content; and teachers understand specific learning and learners. Moreover, four research findings are worth noting. First, the PCK of novice teachers and experienced teachers are significantly different. Second, PCK is a comprehensive knowledge that is skillfully utilized in teaching after teachers synthesizing various kinds of knowledge. Third, PCK is closely related to subject knowledge. Fourth, the PCK of teachers is mainly expressed in the understanding and representation of subject knowledge. In the last section, the authors suggest there is a close relationship between teaching strategies and representation of knowledge, and so does PCK and subject knowledge.