The aim of this study was to describe the relationship between teacher's content knowledge and student's performance in Fraction. This study used the mixed method that provided Content Knowledge test for twelve teachers who taught the seventh class. The test consists of multiple choices to measure knowledge of facts and procedures, knowledge of concepts and relationships, and knowledge of generalization. The study was divided into two phases, Quantitative phase and Qualitative phase. At the Quantitative phase, teachers are mapped in two different levels, low and high based on score of CK test. Two samples were chosen representing each low level and high level. furthermore, two groups/classes are being taught by the sample teacher were selected, by using the Chi-Square test analyzed the relationship between teachers and student performance. At the Qualitative phase of the study included three stages: (1) teacher interview, and (2) Student Problem solving, (3) description of the relationship of teacher's content knowledge and student learning performance. The results of the study show that the Teacher's content knowledge in Fraction is related to student performance, there were similarities in the pattern of student performance tests on fraction and the teacher's answers based on the results of the CK test.