Education reform should be based from teacher's knowledge, it is essential to know what kind of knowledge is needed in teaching before the reform is carried out, and it is still to be studied. This paper mainly studied what kind of PCK (pedagogical content knowledge) math teacher of the junior high school used in teaching. To be more specific, two dependent problems have been studied: what components of PCK which used by teachers in the classroom teaching? How did these different components impacting on teaching?In this paper, PCK is defined as an integration or transformation of the subject knowledge, pedagogical knowledge and context knowledge. Two central components of PCK are: overarching conceptions of subject teaching, learning and teaching knowledge of specific topic. Overarching conceptions of subject teaching include knowledge of both subject content and teaching purposes. Knowledge of subject content includes central concepts, process, knowledge and belief about the nature of subject. Knowledge of teaching purpose is the knowledge and belief of the most valuable to learn for different grades. Learning and teaching knowledge of specific topic includes knowledge of students' understanding, content organization, effects feedback, and instructional strategies. The knowledge of students understanding includes the starting point of students' understanding, the mode of understanding, the level of understanding and typical misunderstanding for specific topic. The knowledge of content organization includes the origin, development and orientation of given topic in the subject system, its horizontal linkages with other subjects. Knowledge of feedback includes effect assess and adjustment of learning methods when students learn the topic. Knowledge of instructional strategies includes selection, organization, representations of teaching content and design of activities for learning.Both content and process of classroom teaching have been evaluated in this study. I investigated not only the effects: how well do the students know those knowledge and skills, but also the process of learning. Mathematics learning process could be divided into five activities, namely, problem-solving, reasoning, communication, connection and representation.16 lessons from 15 junior high school math teachers in Shanghai have been studied by means of video tape observation. The original data was collected by teaching video. The main concerns are the use of PCK in the classroom teaching, students learning activities and learning outcomes.It is revealed that teachers used the above-mentioned six components of PCK in the classroom teaching, which effected teaching differently. The value of teaching on specific topic is decided by the knowledge of both subject content and teaching purposes. The question of student how to learn a specific topic could be answered by the knowledge of students' understanding. The knowledge of content organization compartmentalizes the level of the subject content and determines what to teach. Instructional strategies determine how to teach in according to how the students learn and how to link up related issues. Effects feedback promptly let the students know the results of their study, which could eliminate the misunderstanding.This study revealed that these six components PCK intertwine each other. The overarching conceptions of subject teaching play a guiding role in the knowledge of learning and teaching of specific subjects. With Knowledge of learning and teaching on particular subjects accumulate continually, the overarching conceptions of subject teaching will reorganize, finally qualitatively changed.According to the results of this study, it is recommended that PCK of each typical topic should be summarized by means of analyzing different teaching video tape in the future.