Interactions in the Sun-Earth-Moon System are common misconception for students. Pre-service teacher should develop the lesson plans about the Sun-Earth-Moon system for their professional experience in school. In this work, we investigated understanding of 26 pre-service teachers in the topic of Sun-Earth-Moon system, emphasize on moon phase concept. They studied the earth science, astronomy and space concept learning management course in the first semester of academic year 2016 (August to December 2016). An open-ended question about cause of moon phase is mainly used as research tool. Their responses had been interpreted and categorized into level of understanding by considering key-words, such as, the earth, the moon and the sun. The result revealed that most pre-service teachers have suitable concepts but not all of the components and some of them contain misconception. The founding would be brought into the course for designing lesson plan and tools for improve concept about the moon phase.