<p>Geant4 was created for precise simulation of high-energy physics experiments to explore the origin of the universe. It provides various physical models of hadronic and electromagnetic interactions between particles and matter compared to statistical processing of other simulations. In addition, it is widely used not only in the field of high-energy physics but also in various fields such as cosmic radiation research, astrophysics, and medical physics due to its many types of roles and flexibility. This paper presents the current status and future plan of Geant4 applications for RAON beam. There is a need to study the secondary particles in heavy ion beam and fixed target collision experiments because they have been relatively little concentrated. Using the experiment-optimized physics model, we study physical properties of the primary and secondary heavy ion beams of 20, 40, and 200 MeV/A at the fixed target experiments. These experiments involve ²³⁸U and ¹³²Sn beam with ⁹Be target, as well as ⁴⁰Ar beam with ⁹Be and ¹²C target. We have studied distribution and momentum of secondary particles. These results will help RAON experiment to study secondary particles.</p>