This study aims to determine the relationship between understanding the concept with student learning outcomes through the use of geometer's sketchpad software. This research is quasi experiment research conducted on 88 students class 3 SMAN 1 Pasirpenyu Inhu for 7 weeks. Instruments used in this study is the concept of understanding the exam and test results of learning. This instrument has been tested in preliminary studies to determine reliability and validity. Data ware analysed using pearson correlation statistics. There was a significant relationship between conceptual understanding of mathematics and mathematics experimental group (r = 0.797) and control group (r = 0,721).