The purposes of this study are to determine the ability of learner’s abstraction in understanding concepts and principles of geometry. This study used a qualitative method. The research subjects were selected from undergraduate students of mathematics education. The selection technique is based on the ability to understand geometric concepts. We were collected data through task-based interviews. The analysis of data with the genetic decomposition techniques. Furthermore, the theoretical processes is carried out to determine the characteristics of each level of abstraction. The result was the six levels of students’ ability to understand geometrical concepts. The six levels were: Level 0 (concrete objects), Level 1 (model of semi-concrete), Level 2 (theoretical models), Level 3 (language in domain example), Level 4: (language of the math), and Level 5 (model of inference).