In the 11th-grade Vietnamese Mathematics Curriculum, students learn about parallel relations between planes in space. This is cognitively challenging for many students. Studies have shown difficulties relating to limited spatial imagination and drawing representations. The teacher's approach also causes difficulties for some students; for example, some teachers do not approach new knowledge from practice. These approaches lead students to learn math only in that class rather than to relate math knowledge to real life, whereas real-life objects can be good tools for illustrating knowledge of spatial geometry. This study uses an action research method using GeoGebra 3D Calculator software to design teaching situations about parallel relations of lines and planes in space. This study was conducted with 40 students in 11th grade in Long An Province, Vietnam. It was found that learning tasks can be designed to help students construct knowledge effectively and overcome difficulties. The results of this research show that AR software for 3D Geometry, in particular GeoGebra, creates a connection between reality and abstract knowledge about the parallel relations of lines and surfaces in space. The research also shows that the application of augmented reality in teaching helps students understand and test hypotheses, eliminate false hypotheses, and build new knowledge about parallel relations effectively.