The implementation of cooperative learning model with Snowball Throwing expected to be an alternative to overcome problems, so that students will be interested, active and can improve cognitive understanding of students in learning mathematics. The purpose of this research is to improve cognitive understanding in mathematics, for material circle, knowing the learning environment of students and determine the response class VIII Junior High School in Cianjur. The research method is the Classroom Action Research carried out in three cycles of action. The instrument used is a matter of testing each cycle, the observation sheet of students and teachers in the learning process, questionnaires scale student attitudes and daily journals. The results showed that by applying models of Snowball Throwing learning can improve student learning outcomes. In addition, the students have good learning atmosphere in each cycle and response positively. Based on the results of the study is concluded that Snowball Throwing cooperative learning model can improve cognitive understanding.