Radiation hazard is one of the most critical issues for deep space missions. Among the sources of deep space radiation, the Galactic Cosmic Rays (GCR), which comprise of high energy ions traveling at relativistic speed from outside the solar system, is especially difficult to shield. Hence more efficient shielding materials are necessary for solving the radiation issue in deep space. MULASSIS, a Monte Carlo code developed based on Geant4, is used in this thesis. Dose equivalent analysis is performed with updated radiation weighting factors recommended by ICRP 103 for different shielding materials. Fluence analysis is performed to show the fragmentation and attenuation effect caused by different GCR ions and shielding materials.